Milos Raonic becomes the biggest casualty of the US Open so far

Wimbledon finalist Milos Raonic admits he fell victim to cramp and nerves after he endured a shock defeat to qualifier Ryan Harrison at the US Open.

America’s Harrison is ranked 120th in the world but he took full advantage of his opponent’s discomfort to win 6-7 (4/7) 7-5 7-5 6-1.

Raonic, seeded fifth, had been among the favourites to be crowned champion at Flushing Meadows, after an excellent season that has included reaching the semi-final at the Australian Open and the final at Wimbledon.

The Canadian, however, was hamstrung by cramp, which he said was brought on by anxiety, and it was Harrison who booked his place in round three.

“It was probably just nerves and stress, a mental sort of over-exuberance,” Raonic said.

“Cramping in the left arm, right forearm there towards the end of the third set, both quads, a little bit in the hip flexor on the left. It was just catching me all over.”

Raonic added: “I couldn’t switch grips from one point to the next. There were a few points where I would hold the racquet with my left hand and trying to stretch out my right hand in between shots, and that’s not going to work.”

Raonic becomes the biggest casualty of the US Open so far but it could prove a breakthrough win for Harrison, who was once considered a rising star of American tennis.

Novak Djokovic stands to benefit from Raonic's exit given they were due to meet in the semi-finals and the Serbian enjoyed a far easier passage, after Jiri Vesely withdrew with a left forearm injury.

The walkover comes as a timely boost for Djokovic, who has been struggling with injury himself and he now has an extra day to recover before facing Russian Mikhail Youzhny on Friday.

“I’m very, very disappointed right now,” Vesely said. “Playing Novak, you have to be 100 per cent ready.”

Elsewhere, fifth seed Marin Cilic won through to the third round along with French pair Gael Monfils and Jo-Wilfried Tsonga.

In the last match of the night session, Rafael Nadal coasted past Italian Andreas Seppi 6-0 7-5 6-1.

Roof debut

The one-sided contest was perhaps most memorable for the first closing of the new $150million roof in Arthur Ashe Stadium, after rain began to fall during the second set.

The suspension of play lasted only seven minutes and 22 seconds and Nadal hit the first competitive ball with the construction closed. The Spaniard was also first to practice under the roof last week.

“It is great,” Nadal said. “It’s an unbelievable, unbelievable court.”

Upsets

Meanwhile women’s number three Garbine Muguruza crashed out of the US Open as she was stunned in round two by Latvia’s Anastasija Sevastova.

Sevastova temporarily gave up tennis in 2013 due to illness and injury but she has now reached her first grand slam third round, where she will meet Kateryna Bondarenko.

“I was shaking a little bit at the end,” Sevastova said. “It’s amazing. On Ashe, in a night match, what’s going to be bigger?

“I had to solve my head, my thoughts, what could be, what could not — everything. But I am so happy it went well.”

Former world number one Caroline Wozniacki also recorded an upset as she came from 4-0 down to beat ninth seed Svetlana Kuznetsova.

Wozniacki made a nightmare start and was two points from trailing 5-0 in the first set, but she came storming back to secure a surprise 6-4 6-4 victory.

The Dane climbed top of the world rankings in 2010 but has struggled for fitness and form since and now finds herself placed 74th in the world.