According to atptennis.com Isner served 36 aces against Nieminen. I don't know which site is more credible
I'm quite sure that the stats from the ATP site come directly from the chair umpires' scorecards or nowadays PDAs and other electronic handheld devices. One would think that a good umpire should have a certain edge (very close to the action, paying more attention to the action with all his senses) over sometimes more disinterested or distracted people operating the live scoreboards or collecting the stats for TV purposes at the bigger tournaments. But that's only my theory and it also doesn't matter much for the chair umpire either whether to give an ace for the server or not if he is not totally sure if the ball was barely touched or just not anymore (main thing is he gives the point to the right player).
Carlos --- C'MON Lleyton!!! --- Kiwi!!! --- Jürgen --- Juan
Best of luck to all Germans : Nicolas Kiefer | Rainer Schüttler | Lars | Florian | Tommy
"Most aces served in a row in one game: 5 - Boris Becker (Hopman Cup 1995, vs. A.Medvedev)"
As I recall, Karlovic did the same thing against Haas in his semi from Sthlm Open last year to close out the match. He also flicked a serve just over the net in the first set when Haas was miles behind the baseline trying to return.