MELBOURNE, Australia (AP) – Stefanos Tsitsipas seemed delighted to double the number of subscribers of his YouTube channel to more than 30,000 subscribers in the space of a few hours – "Oh, my God. Really?! "- while he was about to become the youngest Semifinalist Grand Slam since 2007.

Oh, be 20 years old, become the next great tennis achievement and have the opportunity to promote your travel vlogs.

"Guys," he urged netizens to watch the Australian Open Tuesday or on TV, "if you're not subscribed, subscribe."

Lest anyone thinks that Tsitsipas' brilliant victory over Roger Federer in Melbourne Park is a stroke of luck, he continued his momentum by defeating the Spanish Roberto Bautista Agut, 22nd, 7-5 , 4-6, 6-4, 7-6 (2) will become the first Greek player to reach the last four places in a major tournament.

"I knew the win against Federer was important and played an important role in my image – like the one I am," said Tsitsipas, who eliminated the two-time defending champion on Sunday in the fourth round. "But I knew the biggest challenge was the game today, that I could still prove myself.

Of course.

The next champion of Tsitsipas will be Rafael Nadal, 17 times champion of the new generation, the American Frances Tiafoe, 21, dominating 6-3. 6-4, 6-2. Nadal saved the only two points of the encounter that he faced and broke Tiafoe the first time he served in each set.

In the women's action, Danielle Collins, 25, did not sow the colors, reached her first semifinal of Slam with a 2-6, 7-5, 6-1 win over Russia's Anastasia Pavlyuchenkova. Collins was an NCAA champion at the University of Virginia who started the tournament with a 0-5 record in the majors and won five straight wins, including 2016 champion Angelique Kerber.

Collins put aside a bad start on Tuesday, including losing a second 16-minute game, 28 points, 11-Deuce to completely dominate the final set, which she opened by pocketing 20 of 23 points.

She will now face Wimbledon champion Petra Kvitova, who is back in the semifinals for the first time since she was stabbed in an attack at home in December 2016.

"I could not really be back," said Kvitova in tears after beating No. 15 Ash Barty of Australia 6-1, 6-4.

"I call it my" second career, "Kvitova said. "This is the first semifinal of the" second career "."

She had not been so far to a Slam since Wimbledon in 2014, and to Melbourne since 2012.

Encouraged by a strong contingent of Greek flag waving fans, inside and outside the Rod Laver Arena, Tsitsipas presented his array of varied tools, producing 22 aces, 30 winners of more than non-forced errors (68-38) and a flair for getting to the net.

It was a terrific reminder of what he had done against his idol, 37-year-old Federer, a result that prevented Tsitsipas from falling asleep.

Tsitsipas paused in the first and third sets before turning back against Bautista Agut, whose quarter-final thrills included wins over triple-champion Andy Murray and 2014 champion Marin Cilic. US Open the second Federer at Melbourne Park a year ago.

"Well, he's a good player, right? It is very complete. He has a good forehand and a good backhand. It serves well, "said Bautista Agut about Tsitsipas. "I think that he knows the game. He knows how to play.

That's why his peers voted him the most improved player of 2018.

And why he is already in the Top 20, ranked 14th in Australia.

Tsitsipas was recently asked what his goal was for this season. The answer: reach the semifinals at a major. Well, we are all three weeks in 2019 and this box is checked.

So is he satisfied?

"This is the starting point to go further," said Tsitsipas. "It's like the minimum, I'll call it."

No man as young as Tsitsipas had been so far in a Grand Slam tournament since Novak Djokovic at the 2007 US Open or the Australian Open since Andy Roddick in 2003.

"It all looks like a fairy tale, almost. I'm just living this dream, live what I've worked hard for, "said Tsitsipas, who dropped his racket, fell on his back and covered his face with his hands in the end of the match. "I mean, I'm a little moved but not too much because I know I've worked hard to get here."

His parents were sitting in the gallery where his yard was, his father being his trainer; his mother was a tennis player in the Soviet Union – and two siblings, as well as Patrick Mouratoglou, who coaches Serena Williams and plays the role of mentor for Tsitsipas.

Before presenting them, as well as other members of his entourage, to the public during his post-game interview, Tsitsipas spoke of his love for "cinematography, filmmaking, photography" and the how the YouTube videos that he had started doing last year served as a creative place.

Later, at his press conference, Tsitsipas explained what he was getting out of his hobby.

"When I'm desperate sometimes, when I feel depressed, I make these videos. I feel really better, "he said. "It makes me realize that tennis is not the most important thing in life, but that we all have other talents we do not know. It makes me more relaxed. "

___

Follow Howard Fendrich on Twitter at http://twitter.com/HowardFendrich

___

More tennis AP: https://www.apnews.com/apf-Tennis and https://twitter.com/AP_Sports