HONG KONG - No.4 seed Garbiñe Muguruza continued her serene progress through the Prudential Hong Kong Tennis Open draw with a 6-2, 7-5 quarterfinal defeat of the unseeded Luksika Kumkhum.

The Spaniard is yet to drop a set this week, and has now won three consecutive matches for the first time since her run to the Roland Garros semifinals, breaking a streak of seven straight exits in the second or third round. She will next face either No.1 seed Elina Svitolina or No.6 seed Wang Qiang in the last four.

In the first encounter between the two 25-year-olds, both stayed committed to an aggressive strategy both from the baseline and in the forecourt. Muguruza found herself under pressure first, but came back from 0-30 down and saved a break point in the second game before holding with a brace of down-the-line winners, one from each wing.

The former World No.1 used that momentum as a springboard to take a 4-1 lead. Muguruza proved better able to soak up the pace and depth thrown at her, and to sustain her own power over the course of longer rallies; though a handful of loose volley errors hampered her slightly, the two-time major champion conjured up two pinpoint lobs to capture her opponent's serve for a second time.

Kumkhum's shotmaking skills have long meant that she has been a dangerous floater in any draw, despite her relatively light, Asia-centric scheduling over the years, as beaten rivals from Petra Kvitova to Belinda Bencic can attest. The Thai roared as she nailed a double-handed forehand down the line and swarmed the net to positive effect to snatch one break back, but the purple patch was brief: the World No.105's double faults would be an issue for her today, and her third and fourth back-to-back handed the lead over once again.

Muguruza, continuing to keep her offensive play up but her groundstroke mistakes down, would strike 13 winners to 10 unforced errors in the first set and seal it on her second set point as a Kumkhum forehand sailed wide.

A closer second set would find Kumkhum improving her delivery, raising her first serve percentage from 55% to 76% and committing only one double fault. This enabled the two-time WTA semifinalist to protect her serve even as Muguruza pressed relentlessly, emerging with a hold from three-deuce tussles in the first and fifth games without allowing her higher-ranked rival a break point.

But Muguruza was also raising her level, with highlights including an angled backhand pass at full stretch in the third game and improved play at net; when some brilliant scrambling and quick reactions paved the way to the first break for 5-4, having lost just four points on serve in that set so far, the Monterrey champion seemed almost home and dry.

Instead, the stage was set to a thrilling climax to the match as Kumkhum, with her back to the wall, came up with her most dazzling tennis to cling on. Ferocious forehand hitting prevented Muguruza from closing the match out, and a leaping backhand crosscourt winner in the next game raised the real possibility of an unlikely comeback.

But Muguruza remained firm against the sudden onslaught, finding another backhand pass and a heavy off forehand to break again. With Kumkhum's ground game a source of great danger, coming up with 18 winners in total today, the World No.13 opted to bypass it altogether, hammering down consecutive unreturnable serves to close out a compelling battle.