Double Olympic champion Nicolas Massu was seething after he emerged on the wrong end of a marathon battle with Sargis Sargsian and the chair umpire in the second round of the U.S. Open on Thursday.

The 10th seed was docked the first game of the deciding set after throwing his racquet and although he broke back immediately, Sargsian triumphed 6-7, 6-4, 3-6, 7-6, 6-4 in five hours, 10 minutes, the second longest match in U.S. Open history.

Massu, who won a five-set thriller to win the singles in Athens, said the action of umpire Carlos Ramos was inexcusable.

"The first two warnings (a warning and a point penalty) were okay, but the third one, I can't believe it," Massu said.

"I threw my racquet, but all players throw their racquets.

"I didn't lose the match because of that, I lost because I played bad. But it's hard to believe that this guy didn't use his head a little bit.

"This umpire can not umpire any more. This guy's unbelievable."

Massu reached match point at 6-5 in the fourth-set tiebreak, but Sargsian saved it and won the next two points to draw level.

After the altercation at the start of the final set, Sargsian finally broke through in the ninth game and held on to clinch victory.

"I just can't believe I lost. I played for five hours, fought hard and I lost. I am pissed (off) about that."

Sargsian was naturally delighted after equalling his previous best showing at Flushing Meadows.

"It's a huge win for me," Sargsian said. "I haven't had a very good year, so to pull out a match like this, is huge.

"I would quite like it if it rains tomorrow and I can have an extra day off, but I'll be okay."

The Armenian now plays Paul-Henri Mathieu of France for a place in the last 16.