Alex Corretja
At the 1996 US Open, Sampras' path to his fourth title was nearly derailed by Corretja in the quarterfinals before the American escaped in a fifth-set tiebreak. When they next met, in the semifinals of the season-ending championship in 1998, it was Corretja's time to flip the script as he topped the American in a third-set tiebreak. From there, the Spaniard went on to face his countryman, Carlos Moya, who had defeated him in the French Open final that year. After dropping the first two sets, Corretja rallied to win 7-5 in the fifth set, and in the process, became the first champion to triumph who had never captured a Grand Slam singles title.
David Nalbandian
Making his second appearance in three years at the 2005 Tennis Masters Cup, Nalbandian opened up play with a three-set loss to Federer, a rival since their days as juniors. The Argentine bounced back to defeat his countryman Guillermo Coria and Ivan Ljubicic, both in straight sets, to reach the semifinals. After topping Nikolay Davydenko, also in straights, Nalbandian squared off against Federer once again and the world No. 1 took a two-sets-to-love lead behind a couple of tiebreak wins. Nalbandian turned the tables the next two sets to force a decider. It would come down to another tiebreaker, but this time, it was Nalbandian who was victorious, as he picked up the biggest title of his career.
Nikolay Davydenko
As the 2009 season wore on, Davydenko appeared to be getting stronger in the final months of the season. Immediately after the US Open, the Russian triumphed in Malaysia for his third title of the year, then soon followed that up with another trophy lift in Shanghai for his third career Masters victory. There, he defeated Novak Djokovic and Rafael Nadal in his last two matches. Djokovic topped Davydenko in the opening round-robin match at the ATP World Tour Finals, but the world No. 7 then went on a tear, beating Nadal again for the second time that fall, stopping Federer in the semifinals and posting a straight-sets victory over the reigning US Open champion Juan Martin del Potro in the final.