MADRID, Spain - World No.1 Simona Halep made it three routine wins in three matches to reach the quarterfinals at the Mutua Madrid Open, as the two-time defending champion dropped just five games to defeat Kristyna Pliskova, 6-1, 6-4, in the round of 16. 

Halep extended her winning streak in the Spanish capital to 15 straight matches by defeating the left-handed Pliskova sister for the second time in Madrid - having done so in the first round en route to winning last year's title. 

"In the second set, she started to play really well. I think she served much better and I couldn't do much with the return," Halep said after the match. "I served well, too. I feel like it was a very good match, the hardest here. She improved a lot since last year, we played together here, and she was different player.

"I'm really happy I could finish that second set. It's always tough to play against the sisters. I always said that, because they have a strong serve. They can hit the ball very strong, so it's a very good win for me."

Behind 20 winners and 13 unforced errors, Halep broke Pliskova's serve three times in the match, and saved all five break points that she faced on serve.

In the first set, the 26-year-old showed the kind of tennis which saw her drop just four combined games against Ekaterina and Elise Mertens, as she dropped just three points on serve and hit only three unforced errors. 

From 1-1, Halep ran through the last five games of the set, wrestling away a break advantage in Pliskova's second service games of the set - which saw five deuces and five total break points before Halep converted.

The second set proved tighter from the get-go, as Halep was forced to save four of the five break points she saved overall in her first service game of the set.

She also was pushed by Pliskova later on serve, as she faced another break point in the eighth game which would've seen the World No.94 serve to send the match to a decider.

Ultimately, though, Pliskova struck 32 unforced errors to her 18 winners, unable to string together enough points to push the World No.1 to a third set for the first time in three meetings, and dropped the last six points of the contest.

Halep could see a match against Karolina Pliskova up next, as the World No.6 or US Open champion Sloane Stephens will be her quarterfinal foe.

"Both of them are very, very tough opponents. I don't really know who is going to win. The match is open, in my opinion," Halep assessed after the match.

"Stephens is playing really well in this tournament so far. Karolina, the same. So, it doesn't matter against who I play. I know that the match will be very tough and I will be ready. I will focus on myself, like every match, and we'll see what is gonna happen."