1) vs. Navratilova, Wimbledon 1988 final, 5-7, 6-2, 6-1
Navratilova had won Wimbledon for 6 consecutive years (8 titles in total). She had a 47-match winning streak from 1982 until 1988 semis. Many think that she is the best grass-court player ever.
Graf trailed 5-7, 0-2 in the 88 final, changed her racket and simply started to deconstruct Martina who won only one more game. Graf broke Navratilova's serve in all of Martina's last 7 service games. Graf hit 21 direct return winners with Navratilova not even touching the ball (and some more where Navratilova couldn't control Steffi's return). The BBC reporter said that Graf had "lifted women's tennis to a higher level today".
2) vs. Seles, Wimbledon 1992 final, 6-2, 6-1
Seles was uninterrupted #1 for more than 40 weeks and had won the last 3 slams (USO 91, AO 92, FO 92). Graf outplayed and outhit her completely. Seles suffered the worst defeat ever for a #1 in a slam final.
3) vs. Sabatini, Australian Open 1989 semis, 6-3, 6-0
The late Ted Tinling said about Steffi's performance: "I never thought anyone would play as well as Suzanne (Lenglen) . But four times I've seen Martina (Navratilova) when she was better. Then I saw what Steffi did to Sabatini at the Australian Open this year, and that was it. She is better than them all."
Graf's final win at AO 94 (6-0, 6-2) falls into the same category.
The benchmark still today.
Has never been reached again though.