Stefanos Tsitsipas saved three set points before beating Grigor Dimitrov 7-6 (6), 6-4 on Tuesday to join Olympic champion Alexander Zverev in the second round of the Erste Bank Open.
Zverev also advanced in straight sets but had to rally from 5-2 down in the second to overcome Filip Krajinovic 6-2, 7-5.
The top-seeded Tsitsipas, who lost to Dimitrov in the second round last year, was 6-3 down in the tiebreaker before reeling off five straight points to claim the opening set.
Tsitsipas converted his first match point with Dimitrov serving at 5-4 when the 22nd-ranked-Bulgarian hit a forehand wide.
The third-ranked Greek, who is striving for his third title of the season, next plays Frances Tiafoe, who defeated Dusan Lajovic 6-4, 6-4.
Tiafoe beat Tsitsipas in straight sets at Wimbledon this year, but Tsitsipas leads the American 2-1 in career meetings.
Zverev avoided break points against Krajinovic until he was serving for the opening set, but the second-seeded German fought off all three chances for the 40th-ranked Serb.
Zverev lost his serve early in the second but dropped just five more points from 5-2 down to close out the win with five straight games and set up a second-round match against Alex De Minaur.
Casper Ruud and Cameron Norrie, who both are in the race for the remaining two berths at next month's ATP Finals, also advanced with two-set wins.
The fourth-seeded Ruud defeated Lloyd Harris 7-5, 7-6 (2) for his 50th win of the year, and Norrie beat Marton Fucsovics 7-6 (4), 6-1.
Also, the sixth-seeded Felix Auger-Aliassime downed Ricardas Berankis 6-3, 6-2, and Austrian wild-card entry Dennis Novak edged Italian qualifier Gianluca Mager 7-6 (4), 7-6 (4) in a late game.
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