MELBOURNE, Australia — He is the mystery man who few in the sport had heard of just days ago. But Aslan Karatsev of Russia has landed in the semifinals of the Australian Open.

Karatsev on Tuesday became one of the few players to make the final four of a Grand Slam after surviving the qualifying tournament when he beat an ailing Grigor Dimitrov of Bulgaria in four sets, 2-6, 6-4, 6-1, 6-2.

He will face Novak Djokovic, the world No. 1, in the semifinals. Djokovic beat Alexander Zverev in four sets in their quarterfinal on Tuesday night.

Karatsev, 27, was born in Russia and moved to Israel when he was 3. His maternal grandfather is Jewish. He then returned to Russia for his teenage years to pursue better tennis training. That began a meandering journey back and forth across Europe, with stops in Moscow, Germany, Spain and Belarus, where he has been training for three years.

“I was moving around too much,” he said on Tuesday night following his victory.

He has been playing in the tennis hinterlands for several years with little success and even considered quitting in 2017 when he was suffering from a knee injury. He had never qualified for a Grand Slam before this tournament. He won three straight matches at the Australian Open qualifying event in Doha to win a spot in the main event and came in ranked No. 114 in the world. He has never been ranked higher than No. 111.

He has won $618,354 during his professional career. In this tournament, he has already secured a $662,000 paycheck. Another victory would boost it to $1.17 million.

Dimitrov, the No. 18 seed, appeared to have the match under control after the first set but suffered back spasms beginning late in the second set. The pain and stiffness worsened in the third set, and he appeared to be on the edge of retiring for the rest of the match, but returned to the court for the fourth set after receiving medical treatment.

He said his back initially spasmed on Monday and he struggled to put on his socks before the match. “We just couldn’t fix it in time,” Dimitrov said.

Just four other players have made the semifinals of a Grand Slam after getting through the qualifying event.

Ahead of the Australian Open, Karatsev played doubles for Team Russia in the ATP Cup, a team event in which players represent their countries. Russia won the competition, but not because of Karatsev, who lost all three matches in which he played, with two different partners.

His teammates, however, noticed that he was playing as well as they had ever seen, and yet none of them would have predicted anything like this.

“We felt like he could do something amazing,” Daniil Medvedev, Russia’s top player and the No. 4 seed in the Australian Open, said when Karatsev made it through the fourth round. “To be honest, being in your first Grand Slam main draw? Making quarters is something exceptional. He’s not over yet.”

He certainly is not.

After his win set up a meeting with Karatsev in the semifinals, Djokovic said he had not seen Karatsev play before this tournament but has been impressed the last 10 days.

“Very strong guy physically, moves well, has a lot of firepower from the back of the court, great backhand,” Djokovic said. “The Russian school of tennis.”

Karatsev was already the lowest-ranked player to reach the quarterfinals at the Australian Open since Patrick McEnroe in 1991. Karatsev was the first qualifier to make the final eight at a Grand Slam in 10 years.

Karatsev’s magical run in Melbourne began with two victories over lesser players last week, though his second-round win over Egor Gerasimov of Belarus hinted at bigger things to come. Karatsev beat Gerasimov, ranked No. 79 in the world, 6-0, 6-1, 6-0. After that, he dispatched eighth-seeded Diego Schwartzman in three sets. It was an impressive win, but Schwartzman’s best results have come on clay rather than the slick, hard courts at Melbourne Park.

In the fourth round, Karatsev stormed back from two sets down to defeat Canada’s Felix Auger-Aliassime, the No. 20 seed, 3-6, 1-6, 6-3, 6-3, 6-4. Auger-Aliassime is one of the world’s top young players and looked as if he would easily handle Karatsev after the first two sets.

Then Karatsev took a bathroom break. He used the toilet and splashed some water on his face; and when he returned to the court, he found his comfort zone. He began firing aces and winners on his serve with abandon and pushed Auger-Aliassime farther and farther back into the court with his deep groundstrokes.

Karatsev looked to be following a similar script on a warm, humid Tuesday afternoon.

“I was a bit nervous at the start,” he said.

The nerves were certainly justified, but the court he was playing on had an unlikely resemblance to the countless courts where he has competed for years in lower-tier events in front of rows of empty bleachers. On Friday night, health officials instituted a five-day lockdown after more than a dozen people tested positive for Covid-19. There were no spectators other than a few journalists, tournament employees and the players’ support teams.

No one other than Dimitrov and the few people around him knew that he was taking the court at less than 100 percent. Dimitrov, one of the most talented and physically gifted players on the tour, had breezed through his first four matches, including his three-set dismantling of Dominic Thiem, the No. 3 seed.

Karatsev’s nerves showed in the first set, when he made 19 unforced errors and double-faulted three times. In the second set, though, he started standing toe to toe with Dimitrov, playing longer points, sending balls deep into the court and forcing Dimitrov to exert himself and put stress on his back. By the end of the third set, Dimitrov could barely stand.

Less than an hour later, Karatsev was in the semifinals.

“I’m trying to enjoy the moment, not thinking about it too much, just playing from round to round,” he said.

Can he win the tournament?

“We will see,” he said. “How can I say?”

As unlikely as it might seem, Dimitrov said he was not surprised to see Karatsev, who four months ago had a goal of making the Top 100, surging to the final four.

“He’s a great player,” Dimitrov said of Karatsev. “To be here, clearly you’ve done something right. You’ve put in the work; you’ve gone through the qualifiers, went through tough and good matches, built up confidence. There’s so many positives, so why not for him to go further?”