NEW YORK -- While Novak Djokovic's path to the US Open final once appeared strewn with obstacles and tough opponents, it now looks like a free and open highway.

His lucky ride continued Tuesday night when Jo-Wilfried Tsonga retired with left knee pain after dropping the first two sets to Djokovic in a quarterfinal match under the lights of Arthur Ashe Stadium.

That followed a second-round walkover thanks to Jiri Vesely and a third-round, first-set retirement by Mikhail Youzhny.

In total, No. 1 Djokovic has only had to play nine complete sets through five matches heading into Friday's semifinal matchup with No. 10 Gael Monfils of France. By Friday, Djokovic will have completed just one full match in an 11-day span.

"I put myself in a position again to be one match away from the finals," said Djokovic, who won the Open in 2011 and '15 and is seeking his 13th career Grand Slam crown. "As [the] tournament progresses, I feel like I'm getting better. Of course this Grand Slam is very unique for me. I never experienced something like this to have three retirements on the road to the semifinals.

"I can only wish all of my opponents a speedy recovery. That's all I can do on my end. I obviously try to focus on things that I need to do; stick to the game plan."

Djokovic entered the Open with a balky left wrist that he injured right before the Rio Olympics and contributed to his first-round loss to eventual silver medalist Juan Martin del Potro.

The wrist injury impacts his two-handed backhand, but because of his easy path to the semifinals -- and the additional rest he will get before Friday's semis -- Djokovic says he's feeling pretty healthy.

"Actually, in this stage of the season, considering some physical issues I have had in the last month, month and a half, this was the scenario that I needed and I wished for," he said. "I got a lot of days off and recovered my body. Right now I'm feeling very close to the peak. That's the position where I want to be."

On top of all this, the draw has fallen the Serb's way, too.

When the draw first came out, Djokovic faced the prospect of having to beat three former Open champions to win the title: 2014 champ Marin Cilic in the quarterfinals, two-time winner Rafael Nadal in the semis and 2012 champion Andy Murray in the finals.

But American Jack Sock took out Cilic in straight sets in the third round, and Frenchman Lucas Pouille stunned Nadal in a five-set, fourth-round epic.

Monfils, playing a highly disciplined and focused brand of tennis, then dispatched Pouille in straight sets in the quarterfinals, setting up the semifinal with Djokovic. The Serb is 12-0 all-time against the Frenchman.

"He seems more focused at this time of his career," Djokovic said of Monfils. "Especially on the hard court this year maybe he's playing the best tennis he ever played. He's very consistent. He hasn't dropped a set till semis. That says a lot about the level he's on."

Said Monfils: "I have a second opportunity to get to my first slam final, and the opportunity to maybe beat him for the first time in the main tour, to beat the world No. 1."

While Djokovic hasn't had to meet a Grand Slam champion yet in this tournament, three major champions are slugging it out on the other half of the draw.

No. 2 Murray, coming off winning Wimbledon and the Olympics, both for a second time, was set to meet No. 6 Kei Nishikori in Wednesday's afternoon quarterfinal.

The night match features what figures to be a highly entertaining affair between No. 3 Stan Wawrinka, a two-time major winner, and unseeded Juan Martin del Potro, the 2009 Open champ who is riding high after undergoing multiple wrist surgeries.

Most observers expect a Djokovic-Murray final, which would be their third Grand Slam final of the year after the Serb beat the Scot for the Australian and French Open championships.

Djokovic is 24-10 all-time against Murray, having won five of the last six.

With two more match wins, Djokovic will capture his 13th career Grand Slam title, putting him one behind Nadal and Pete Sampras, both of whom won 14, and four behind Roger Federer's all-time men's mark of 17.

"I'm really looking forward to come out on the court on Friday in semifinals," he said.

Follow Adam Zagoria on Twitter @AdamZagoria for updates throughout the U.S. Open.