Agassi won a contest, which lasted two hours 48 minutes, 7-6, 4-6, 6-2, 6-3 when his opponent hit a backhand return of service long, stretching his unbeaten run against Stich to six matches.
The 24-year-old American, who climbs two places in the ATP rankings to eight, outwitted Stich, 26, with sharp service returns, stinging passes and cunning lobs.
Stich hit 18 aces and his backhand worked well for much of the match, but he was often caught out rushing the net by Agassi. 'Michael Stich is a very tough player indoors, and he started off serving so well and I was a little bit lucky to get back into the first set,' Agassi said afterwards. 'In the second I got a little tired, but I pulled it back together and played really well to win.'