Russian Andrey Rublev used a steady stream of power from the baseline to upset eighth-seeded Greek Stefanos Tsitsipas 6-4, 6-7(5), 7-6(7), 7-5 on Tuesday and reach the second round of the U.S. Open.

World number 43 Rublev, who two weeks ago earned the biggest win of his career when he beat Roger Federer in the third round at Cincinnati, attacked Tsitsipas with a barrage of all-in forehands and broke his opponent five times in the match.

Rublev displayed near flawless judgment with his shotmaking throughout the match and while Tsitsipas tried to lure him off the baseline, the Russian stuck to his gameplan to prevail in a battle of 21-year-olds that lasted nearly four hours.

“Both of us were tired. He started to cramp ... I was cramping in the match and tried not to show it,” said Rublev.

“When you win matches like this it gives you lots of confidence.”

Losing cool

Tsitsipas, whose best showing at a Grand Slam came this year in Australia where he reached the semifinals, received a coaching warning for his dad's behaviour early in the third set at Louis Armstrong Stadium.

The Greek, one game after receiving a time violation in the fourth set, then became furious when the umpire would not allow him extra time on the changeover to change his bandana.

An angry Tsitsipas told the umpire: “You're a weirdo, you're all weirdos.” He also asked to be given a point penalty, which the umpire granted at 3-4 before Rublev went on to hold to love.

Tsitsipas showcased a well-rounded game that featured solid serves, relentless forehands and plenty of trips to the net but Rublev took his game to a higher level.

The Russian played predominantly at the baseline, pounding groundstrokes and stinging forehands that zipped by Tsitsipas and painted the lines.

Tsitsipas seemed to hurt his left wrist when he used it to brace himself from falling hard to the court after reaching for a backhand volley in the opening game.

But the Greek, who has a one-handed backhand, seemed mostly unbothered when play resumed but was unable to slow down an in-form Rublev.

Up next for Rublev, who reached the U.S. open quarterfinals in 2017, will be either Frenchman Gilles Simon or American wildcard Bjorn Fratangelo.

Pospisil stuns Khachanov

Canada's Vasek Pospisil upset Russian ninth seed Karen Khachanov 4-6, 7-5, 7-5, 4-6, 6-3 on Tuesday to reach the second round of the U.S. Open.

Pospisil, who has fallen to 216th in the world rankings this year after having back surgery in January that sidelined him until Wimbledon, fired 15 aces and broke Khachanov four times during the nearly four-hour encounter.

The 29-year-old Canadian, who has never advanced past the second round in New York, will next face unseeded American Tennys Sandgren, who beat Frenchman Jo-Wilfried Tsonga.