By Fatih Erel

ISTANBUL

Defending champion and No. 1 seed Rafael Nadal pulled through what was otherwise a disastrous start to US Open finals against No.9 Dominic Thiem to claim a semifinal berth.

Losing the first set 0-6, Nadal managed to come back 6-4, 7-5, 6-7, 7-6 in the epic five-hour battle that finished in the early hours on Wednesday in Arthur Ashe Stadium, New York.

"I told him that I am very sorry and you are very good," Nadal said of the 25-year-old Austrian.

"It is going to be stuck in my mind forever. Forever, I am going to remember this match, for sure," Thiem said after the match.

"It is cruel sometimes, tennis, because I think this match did not really deserve a loser. But there has to be one."

In Friday's semi-finals, Nadal will play the 2009 champion, Argentinian Juan Martin del Potro.

Six-time champion Serena Williams in semifinals

The 36-year-old Williams toppled Czech Karolina Pliskova with 6-4 6-3 in two sets to reach the semifinals for a ninth consecutive time.

"I was having a baby at this time last year so I really have nothing to prove," Williams said after the match.

"The crowd was really for me and I felt so bad that I was not winning," said Williams.

On Friday, Williams will play against Anastasija Sevastova of Latvia, who beat defending champion Sloane Stephens.