Washington - Third-ranked defending champion Alexander Zverev reached the Washington Open final on Saturday by defeating Greek teen Stefanos Tsitsipas 6-2, 6-4 to launch the first all-21-or-under ATP semi-finals in 23 years.
Germany's Zverev, the oldest of the last four at 21, will play Sunday for the $384,120 (331,637 euros) top prize against the later winner between Russian Andrey Rublev, 20, and 19-year-old Australian Alex De Minaur.
Not since 1995 at Buenos Aires had the ATP seen a completely 21-and-under semi-final and it's a first in the Washington event's half-century history.
Top seed Zverev could join a Washington back-to-back champions list that includes Argentina's Juan Martin del Potro (2008-09) plus Americans Andre Agassi (1990-91 and 1998-99) and Michael Chang (1996-97).
Zverev seeks his ninth career ATP title and third of the year after Munich and Madrid. He also was runner-up at Miami and Rome.
Tsitsipas, 19, is ranked a career-high 32nd. He became the first Greek ATP finalist in 45 years in April at Barcelona. Last month at Wimbledon, he became the first Greek in the last 16 at any Open era Grand Slam.
Zverev broke in the third and fifth games of the opening set, which he took in 34 minutes with his third of five aces, then broke Tsitsipas again on his fourth chance during an epic 15-minute ninth game of the second set. Zverev held a final time to settle matters after 88 minutes.
Neither De Minaur nor Rublev have beaten Zverev, the Aussie falling in a Davis Cup fifth-set tie-breaker earlier this year and Rublev losing in straight sets in 2016 at Monaco and last year at Beijing.
Rublev beat American Denis Kudla 6-1, 6-4, in a quarter-final delayed from Friday by rain. Rublev, ranked 46th, was a shock US Open quarter-finalist last year and only in July returned from a three-month layoff due to a lower back stress fracture.
"I'm really happy," Rublev said. "An injury takes time. You can't do anything. It's really tough. But as soon as I started practicing I tried to get back as fast as I can."
Rublev, who won his only ATP title last year at Umag and made his second career final in January at Doha, needed only 74 minutes to dispatch 85th-ranked local hero Kudla.
De Minaur advanced by walkover when three-time Grand Slam champion Andy Murray withdrew Friday after his third grueling three-set victory in four days. Murray was in only his third event back after an 11-month spell out of action due to a right hip injury.
In the companion WTA event, two-time Grand Slam champion Svetlana Kuznetsova of Russia advanced by defeating Kazakh eighth seed Yulia Putintseva 6-2, 6-2 in a quarter-final rained out Friday.
World number 128 Kuznetsova, the 2004 US Open and 2009 French Open champion as well as a 2014 Washington winner, booked a semi-final against Germany's 91st-ranked Andrea Petkovic.
In the other women's semi-final, Croatian seventh seed Donna Vekic - who eliminated Poland's Magda Linette 6-1, 7-6 (7/0) - will meet China's 85th-ranked Zheng Saisai, who beat US qualifier Allie Kiick 6-3, 6-1.
Alexander Zverev (GER x1) bt Stefanos Tsitsipas (GRE x10) 6-2, 6-4
Andrey Rublev (RUS x16) bt Denis Kudla (USA) 6-1, 6-4
Svetlana Kuznetsova (RUS) bt Yulia Putintseva (KAZ x8) 6-2, 6-2
Donna Vekic (CRO x7) bt Magda Linette (POL) 6-1, 7-6 (7/0)
Zheng Saisai (CHN) bt Allie Kiick (USA) 6-3, 6-1