Rafael Nadal won a tricky contest in straight sets ©Getty Images

Rafael Nadal won an intriguing encounter against Diego Schwartzman in straight sets to reach the semi-finals of the US Open at Flushing Meadows.

The Spanish second seed, bidding for a 19th grand slam title and a fourth in New York, raced to a 6-4, 7-5, 6-2 success at Arthur Ashe Stadium.

Thirty-three-year-old Nadal is favourite to win the tournament after Roger Federer was knocked out and Novak Djokovic's withdrawal through injury.

But he made harder work of the 20th seed than was necessary, allowing the Argentine back into the opening two sets having been a double break up.

Nadal also needed treatment to his left arm in the final set but blasted some fine winners as he made the US Open semi-finals for the eighth time.

Schwartzman, who has regularly trained at the Rafael Nadal Tennis Academy in Mallorca, made sure the match lasted nearly three hours despite not pinching a set.

"I am super happy in the way that I accepted the situation," said Nadal, who hit 39 unforced errors, four more than Schwartzman.

"Here I am, in semi-finals, and that's super important for me. 

"It means everything."

Nadal will meet surprise semi-finalist Matteo Berrettini next, after the 24th seed outlasted France's 13th seed Gaël Monfils in a five-set epic.

The Italian came through 3-6, 6-3, 6-2, 3-6, 7-6 to reach his this stage of a grand slam for the first time.

He had only previously made the quarter-finals of one hard court tournament, in Sofia in February.

The 23-year-old missed out on five match points in the last, before eventually finishing the job 7-5 in a tiebreak.

Canada's Bianca Andreescu continued her fine run to make the last four ©Getty Images
Canada's Bianca Andreescu continued her fine run to make the last four ©Getty Images

In the women's draw, Canada's 19-year-old Bianca Andreescu continued her dream run into the last four having never previously made it past round two of a grand slam.

The 15th seed came from behind to beat 25th-seed Belgian Elise Mertens, 3-6, 6-2, 6-3.

"This is honestly so crazy," said Andreescu. 

"What I've accomplished this year, I'm speechless. 

"I need someone to pinch me right now."

The Canadian will now meet Switzerland's 13th seed Belinda Bencic, who knocked out Croatia's 23rd seed Donna Vekić 7-6, 6-3.

Like Andreescu, Bencic will also be playing in a first grand slam semi-final.

Both of the women's semi-finals are tomorrow.

On the other side of the draw, American great Serena Williams will take on Ukraine's Elina Svitolina.

Williams is favourite for a seventh US Open title and a 24th grand slam in total.