DOHA, Qatar - American qualifier CiCi Bellis claimed the biggest win of her career after taking down defending champion Karolina Pliskova in straight sets to reach the quarterfinals at the Qatar Total Open.

Bellis read the Czech’s booming serve perfectly, breaking her five times en route to the 7-6(4), 6-3 victory in an hour and 37 minutes. Even more impressive, her victory over World No.5 Pliskova is Bellis' first Top 5 win of her career.

“This was huge for me,” 18-year-old Bellis said in her on-court interview. “I think I played a really good match and just tried to track down as many balls as I could. Obviously, I’ve watched her play for many years and she’s one of my idols for sure. I’m just really happy to was able to get through it.”

It was their second meeting of the season after Brisbane, where Pliskova won comfortably in straight sets dropping just two games.

“When I played her in Brisbane, she killed me, and I was super nervous before that match,” Bellis recalled. “It was the start of the year. It was my second match of the year and she was playing really well there.

“I knew I had to be super on top of it from the first point today, and that's what my team and I discussed, from the first point I had to be 100 percent rather than kind of get into the match and take a few games. So I think that was a big part of it.”

The story was completely different story today, with qualifier Bellis coming into the matchup after dealing upsets to Daria Kasatkina (who retired in the second set with a neck injury) and No.12 seed Madison Keys.  

Pliskova, who came to Doha after Fed Cup and is recovering from an illness, spoke of feeling low energy levels coming into the match. It showed against the 18-year-old, and she couldn’t seem to find her rhythm againsts Bellis’ relentless attacking.

Bellis kept Pliskova under pressure from the start of the match, coming away with the edge after three straight breaks of serve. The momentum swung between the two as they traded five more breaks to stay level and bring up a tiebreaker. Despite Pliskova finding some of her biggest serves of the set in the tiebreak, Bellis had the answers to force error after error and edge through the opening set.

While the first set featured a dizzying eight breaks of serve, the second was decided by just one. Bellis converted on her fifth break chance of game six to grab a 4-2 lead and held onto it for the rest of the match, serving out the biggest victory of her career after an hour and 38 minutes.

“I think it's definitely a milestone,” Bellis said. “It's great, but you know, definitely move on to the next one and just start thinking about tomorrow.

“When you're playing girls ranked this high, you can't really think about it. You just have to kind of play the ball. I've just been trying to take it one point at a time, one game at a time one and one match at a time.”

Bellis stayed aggressive throughout the match, hitting 17 winners and 26 unforced errors across two sets. Pliskova struck 30 winners - almost double the amount of her young opponent - but was undone by her 53 unforced errors and eight double faults.

The victory earns Bellis a matchup against No.2 seed Simona Halep in the Doha quarterfinals.