To answer the question, the decision was indeed controversial... but accounts of the fight I find are split on whether or not Rocky really won or not.
Here's one that says Rocky won:
http://www.boxingnews.de/news/001_Rocky_vs_Nunn.html
BERLIN, 21st March 1998.
Ringside Report by Fabian Weber
Pugilists from the early era of boxing would have been proud of the tough Italo-German Graciano Rocchigiani. Despite suffering from a serious virus infection only one month ago, and despite the fact, that he and his trainer had finished their relation just some days before the fight, Rocchigiani soundly outfought American Michael Nunn to capture the vacant WBC Light Heavyweight title.
Graciano Rocchigiani and Michael Nunn were already scheduled to fight on February 7th, when the ringside doctor diagnosed 38.8°C feaver and a serious virus infection on Rocky, only hours before the event should begin. Promotor Wilfried Sauerland decided to postpone the whole event - much to the disappointment of some thousand fans, who had come to the Max-Schmeling Halle in Berlin to no purpose.
After getting past his sickness, which caused Rocchigiani to lose 9 pounds, he quickly suffered his second set back during his training in Miami. In contrast to Rocky’s expectations, his American trainer Emanuel Steward wasn’t the much anticipated help he would have needed to regain his physical and psychological shape. „Steward almost didn’t work with me at all“, the angry German complaint. „Most of the time he just concentrates on Lennox Lewis.“ So the former IBF super middleweight champion decided, it was better just to rely on himself, to return to Germany and to finish his training alone - only with the help of his brother Ralf, a former WBO Cruiserweight title holder.
Because of all these disadventageous events, most German experts awaited the fight of their countryman sceptically. But this situation not only wasn’t new for Rochigiani; it was the general feeling he was used from all his four tries to capture a world title in the last four years. Since 1994 Rocchigiani had challenged four undefeated world title holders: He dropped a disputed decision to Chris Eubank, twice went 12 competitive rounds with Henry Maske, and was again the victim of a disputed decision, when the WBO disqualified him after he had knocked out his countryman Dariusz Michalczewski with an illegal punch.
Everytime Graciano Rocchigiani had given his opponnent his thoughest test so far, and everytime he had proven the sceptics wrong. But even though: Everytime he didn’t come away with the title also.
This finally changed, when Rocky fought former two division champion Michael Nunn in Berlin. The American came from a nine fight winning streak, which seemingly looked too dangerous even to Roy Jones, who refused to defend his title against Nunn, his mandatory challenger.
The drastic difference in styles of the two world class southpaws made this matchup an eventfull and exciting fight for the 10,500 German spectators, who enthusiastically cheered for their countryman.
The slick and highly movable Nunn circuled around his opponent and scored with quick combinations en route to win the first two rounds. Hit by a jab the German, who proved to be highly vulnerable to face injuries several times in his career, suffered a bleeding cut above the eye.
From the third round on, though, Rocchigiani effectively came into the fight, moved his opponent against the ropes and landed precise hooks at close range. Even though Nunn, the 1984 Olympic Silver medalist, still possesses his quick hands and feet, his defensive has worsen decisively. When the fight went on, Rocchigiani found his opponent easily to counter, either with his stiff southpaw jab or with a hard left cross.
On many occasions the American gave Rocchigiani additional help to land punches, when he leaned back into the ropes, lowered his hands and arrogantly taunted the German. But Nunn’s reflexes are not good enough anymore to allow him these kind of games. Repeatedly the German snapped back Michael Nunn’s head, drove him into the corners and wobbled his knees. Nunn’s repeated tries to regain the momentum with soft multiple-punch combinations didn’t seem to bother Rocchigiani, as most punches either landed on Rocky’s high guard or just missed due to the effective peek-a-boo defense of the German.
Although not even the long silenced Nunn-supporters, who were outnumbered 1,000 times by German fans in the Max-Schmeling Halle in Rocky’s home town, had any doubts who was the winner, the decision was split. The judges ruled the bout 118:111 and 115:113 for the German and 116:113 for Nunn.
Only manager Dan Goosen found a reason to complain: „The German comissioners have acted illegally.“, Goosen defiantly pretended after the fight. „They slipped Rocchigiani’s corner the judges’ scores between rounds.“ Even if this would be true, it’s completely unlogically to assume, that this impoliteness had any impact into the outcome of the fight. Goosen, who announced he would file an official protest, was probably rather angry with himself, that he hadn’t been clever enough to arrange the same service for his fighter, too.
„I thought I won the fight, but the judges saw it differently“, a disappointed Nunn explained after the fight. „I landed more blows, probably three-to-one“, he pretended. In fact the American threw at least twice as many punches as Rocchigiani. But it was hard to find at least one significant blow of Michael Nunn per round. Stable mate and former 130 lbs champ Gabriel Ruelas, who was sitting ringside, also shook his head when the bout was over. But the more objective Mexican world class fighter was rather disappointed about Nunn’s performance and didn’t see a reason to dispute the decision.
Graciano Rocchiani, who won his first world title fight since 1989, had found himself in the twighlight of his career, when he stepped into the ring in Berlin. Now the new two-division champion has a bright future in front of him. „This is a special feeling for me today. I’m endless happy.“, an excited Rocchigiani said after the fight. „This WBC title is the greatest for me. This was the ultimately last train I could jump on.“, the 34-year old German admitted.
With a fax mail from Mexico WBC president Jose Sulaiman had restricted before the fight, that the winner has to face former WBC title holder Roy Jones Jr. next. But this seems to be rather a restriction to Jones than to the victorious German, as the former pound-for-pound king showed reluctance to step into the ring at all anymore.
The fight most Germans want to see is a rematch between Rocchigiani and WBO title holder Dariusz Michalczewski, who had successfully defended his title the evening before with a stunning fourth round KO of Italian Andrea Magi. As both seem willing to take on each other again, only the cooperative work of two rival promotors and two rival TV-station are standing in between this interesting rematch. But the past has proven, that these obstacles can be enough to prevent a fight, even if the public demands it aggressively.
Meanwhile one must honestly grant Rocchigiani his world title, after he suffered enough set backs in his past to fill three lives. And unquestionable the Geman has enriched the boxing world with a colorfull new world champion.
Rocchigiani: 40-4-1 (19), 174
Nunn: 52-4 (34), 174
And another...
http://www.s-t.com/daily/03-98/03-22-98/zzzspcap.htm
Germany's Graciano Rocchigiani pounded American Michael Nunn over 12 rounds Saturday to win the WBC light heavyweight title in a close fight ruled a split decision by the judges.Nunn landed far more blows against Rocchigiani, slipping jabs repeatedly through the German's closed peek-a-boo defense in the bout for the title vacated by Roy Jones Jr.But it was Rocchigiani, a former IBF super middleweight champion, who rocked Nunn with the harder punches, snapping the faster American's head back during the in-fighting and on the ropes.The judges ruled the bout 118-111 and 115-113 for the German fighter and 116-113 for Nunn in a high-tempo fight that often had the 10,500 spectators roaring.
But they're both directly contradicted by articles like this...
http://www.freep.com/sports/othersports/qboxing6.htm
Many thought he deserved better than the split-decision loss in his Berlin battle last year with Germany's Graciano Rocchigiani for the interim WBC title.
...and this...
http://www.cdesports.com/ampres.html
Nunn lost a controversial split decision that seemed more of a hometown decision.
So in the end, the fight appears to have been one of those "What you like more..." scenerios. There were apparently some people who share your assessment of the fight, but others who disagree strongly.
BTW, here's what Nunn said of the fight (whatever that's worth):
From
http://www.qctimes.com/sports/980901_story8.html
"I'm still a little PO'd," Nunn said...
"When a million people tell you that you won the fight, you've got to wonder," Nunn said of the fight that a Mexican judge scored 116-113 in his favor.