New York (CNN) The unlikeliest semifinalist at the US Open this year?

No, it's not Matteo Berrettini, who ousted Gael Monfils in five thrilling sets Wednesday to become the first Italian men's semifinalist here since 1977.

The distinction might just belong to Grigor Dimitrov, even if the suave Bulgarian -- nicknamed 'Baby Fed' due to his Roger Federer-esque strokes -- had already been to a pair of grand slam semifinals at Wimbledon in 2014 and the Australian Open in 2017.

Dimitrov entered the US Open ranked 78th -- his lowest figure at a major since the 2012 French Open -- and lost seven of his last eight matches entering the season's final major.

One of those came against Kevin King, who was ranked 405th when he downed Dimitrov to open the US Open Series of hard-court tournaments in Atlanta in July.

It was a bad slump.

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Who, then, could have foreseen Dimitrov upsetting pal and sometimes singing buddy Federer -- albeit an ailing one -- in the quarterfinals and reaching the last four in New York?

Not even Dimitrov himself, as it turned out.

"Me, too," he agreed with a reporter Tuesday who said he didn't expect the 28-year-old to go this far after he'd fallen to King two months ago.

Ranking tumbles

Although Dimitrov has never really fulfilled expectations -- perhaps they were always too high, since his shots might resemble Federer but don't have as much sting, especially on the backhand -- a ranking below 50th looks strange for someone of his still plentiful ability.

Here was the man who won the year-end championships as recently as two years ago, surging to No. 3 in the world.

A shoulder injury was the big reason his ranking, and confidence, tumbled this year, only to be restored at precisely the right time for him.

Following the injury, he might feel getting a walkover in the second round against 12th seed Borna Coric, a navigable draw to the quarterfinals and Federer's back and neck injury were the considerable dose of luck he was owed.

"I think the past six, seven months have been pretty rough for me," said Dimitrov, well liked by his peers. "But I had somebody to lean on, my friends, my family.

"I kept on believing again in the work, the rehab I had to put behind my shoulder, the exercise, the practice, fixing up the racket a little bit. There were so many things I had to adjust in such a small but big period of time.

"Next thing you know, you're almost end of the year, you have a result like that. It's pretty special to me."

Pretty special and in another way, pretty rare, since Dimitrov admitted he is in New York without coaches Andre Agassi and Radek Stepanek, the pair who formerly guided world No. 1 Novak Djokovic.

It could get even better for Dimitrov, who is sure to return to around the top 25 after the US Open.

A chance against Medvedev?

On paper he won't be favored against one of the tour's most in-form players in fifth-seed Daniil Medvedev on Friday, but the Russian who has played villain for most of the US Open is dealing with an array of injuries.

The latest one was a quadriceps issue sustained in a four-set win over Stan Wawrinka in what was a double blow for Swiss fans Tuesday.

One of the two will land in a maiden grand slam final.

Djokovic and Federer's exits mean that two of the so-called "Big 3" didn't make the semifinals. The only one left: No. 2 Rafael Nadal, who defeated Diego Schwartzman in Wednesday's night session.

Still, for Dimtrov, 24th-seed Berrettini and Medvedev, it might feel the men's title could be up for grabs.

The big-serving Berrettini converted on his fifth match point to knock out 13th-seed Monfils 3-6, 6-3, 6-2, 3-6, 7-6(5) in three hours, 57 minutes.

Matteo Berrettini celebrates after beating Gael Monfils to reach the US Open semifinals.

The French showman initially had a set and break advantage but eventually came unstuck, hitting 17 double faults and two in the tiebreak in a battle that ended under the roof due to rain on a steamy New York day.

Mind you, Berrettini, 23, hit one himself on his first match point at 5-4 in the fifth, paving the way for a nail biting conclusion.

Women's semifinals are set

Serena Williams is the women's favorite, with her bid for a record-equaling 24th grand slam title continuing in the semifinals Thursday against Monfils' girlfriend, No. 5 Elina Svitolina.

Belinda Bencic became the first women's semifinalist from the top half of the draw when the No. 13 seed edged No 23 seed Donna Vekic 7-6(5), 6-3 to start play Wednesday at Arthur Ashe Stadium. The match turned when Vekic -- appearing in her first grand slam quarterfinal -- couldn't serve out the first set at 5-4.

Bencic will face No. 15 Bianca Andreescu, with the 19-year-old Canadian grinding out another win: 3-6, 6-2, 6-3 against No. 25 Elise Mertens of Belgium in just over two hours. Andreescu is the fourth woman to reach the semifinals in her US Open debut, joining Chris Evert, Pam Shriver and Venus Williams.

It will be the first meeting between Bencic and Andreescu.