Grigor Dimitrov of Bulgaria celebrates his five-set upset of five-time champion Roger Federer in the men's singles quarterfinals of the 2019 US Open in New York City. (AFP)

NEW YORK—Grigor Dimitrov rallied for a shocking upset of 20-time Grand Slam champion Roger Federer at the US Open on Tuesday, the lowest-ranked New York semifinalist in 28 years advancing to face Daniil Medvedev.

The 78th-ranked Bulgarian, who had dropped all seven prior meetings with Federer, made a dramatic fightback to defeat the Swiss third seed 3-6, 6-4, 3-6, 6-4, 6-2 at Arthur Ashe Stadium and will face Russian fifth seed Medvedev in Friday’s semifinals.

Medvedev advanced to his first Grand Slam semifinal by defeating three-time major winner Stan Wawrinka 7-6 (8/6), 6-3, 3-6, 6-1.

“I’m really happy to be in my first semifinal,” Medvedev said.

Medvedev struggled with a sore left quadriceps muscle that had him think about quitting the match in the first set.

“Before the match I was feeling perfect. In the first set I think I pulled my quadriceps,” Medvedev said.

“I had a really big pain in my quadriceps and thought I wasn’t going to continue the match.”

Medvedev took a medical timeout and had the area taped and took a painkiller.

“In the fourth set, I started feeling the painkiller and started moving better,” he said. “For sure I hope to be ready for the semis.”

Medvedev, at 23, becomes the youngest US Open semifinalist since Novak Djokovic in 2010 and Russia’s first Slam semifinalist since Mikhail Youzhny at the 2010 US Open.

Serena Williams moves within a victory of a 10th US Open final, 20 years after winning her first Grand Slam title in New York. (AFP)

Serena Williams earned her 100th win at the US Open with a brutal 44-minute demolition of Wang Qiang, firing an ominous warning to rivals in her pursuit of a record-tying 24th Grand Slam title.

The six-time US Open champion dismantled the Chinese 18th seed 6-1, 6-0 in a complete mismatch that was the quickest at this year’s tournament to set up a semifinal clash with Ukrainian trailblazer Elina Svitolina.

Williams brought up a century of US Open wins to move to within one of the all-time leader Chris Evert.

“It’s really unbelievable, literally. From when I first started here, I think I was 16, I didn’t think I would ever get to 100. I didn’t think I would still be out here,” Williams said.

The 37-year-old American is seeking a 24th major title to match Margaret Court’s longstanding record, and smacked 25 winners against first-time Slam quarter-finalist Wang, who failed to hit a single one.

The 27-year-old Wang had not lost a set during her best Slam run that included a defeat of reigning French Open champion Ashleigh Barty in the last 16, but she was powerless to stop a Williams onslaught at Arthur Ashe Stadium.

“When I play someone who is playing really well, I know I have to either step it up or go home and I wasn’t ready to go home. I had to come out here and play really well,” said Williams, suffering no ill effects from the ankle she rolled in her previous match.

“Physically I’m feeling great. More than anything I’m just having fun every time I come out here.”

Wang, trying to become just the fourth Chinese player to reach the last four of a Slam, won just four points in the second set and 15 in total.

“It’s not easy to play against her,” Wang said. “The power, like, I cannot handle it. Just too much for me.”

Williams captured her last Slam title at the 2017 Australian Open while pregnant and hasn’t won the US Open since 2014.

Fifth seed Svitolina defeated Britain’s Johanna Konta 6-4, 6-4 to become the first Ukrainian to reach the US Open semifinals, matching her run to the last four at Wimbledon in July.