MIAMI, FL, USA - No.5 seed Karolina Pliskova moved into the Miami Open quarterfinals for the third time in her career when Zarina Diyas was forced to retire injured while trailing 6-2, 2-1 in the first of the day's fourth round encounters.

Last year's semifinalist had been stretched all the way in the previous round by Hsieh Su-Wei, taking two hours and 24 minutes to battle past Chinese Taipei's No.1 player, but was efficient and ruthless straight out of the blocks today. "I felt good in my tennis, much better than my last match," Pliskova assessed her form afterwards.

A Diyas double fault on the very first point set the Kazakh player off on the wrong foot immediately, and two points later Pliskova's first winner of eight over the first set gave the 26-year-old her first break point opportunity - duly seized as Diyas sent a backhand long.

This pattern would characterise the opening set. The Czech player was sharp in pouncing on any Diyas groundstroke that dropped just a bit too short; with that pressure in mind, the World No.56's usual steadiness wobbled. Her attempts to pin Pliskova behind the baseline simply led to more mistakes from her own racket - committing 16 unforced errors in total in the first set.

The former World No.1's famous serve, meanwhile, provided a solid foundation for her game: indeed, Pliskova would not drop a point behind her first service today.

After only 18 minutes, the 2016 US Open runner-up had stormed her way to a 5-1 lead and her first set point. It was at this point, though, that Diyas managed to halt what had seemed like a rout to briefly put her stamp on the match.

The former World No.31 would save two set points in that game and two more in the next, beginning to move the ball around the court with more authority and forcing Pliskova to summon up her finest serves to eventually put the set to bed on her fifth set point after 35 minutes.

Diyas would carry this form over into the start of the second set, firing a sequence of spectacular down-the-line winners to hold in the opening game. However, last year's Japan Open champion had taken two medical time-outs already and was visibly struggling with her movement.

Though she managed to stave off two more break points in her next service game with brave winners, a netted forehand ultimately conceded the break - and two points later, Diyas would be unable to continue.

Pliskova was grateful for the abbreviated time spent in the Florida heat. "I played an hour, which is quite OK," she mused. "It's good that I saved energy for tomorrow's matches." 

Pliskova, who has now made the quarterfinals or better in five of her six tournaments this year, will take on either No.30 seed Agnieszka Radwanska or returning former World No.1 Victoria Azarenka in the last eight - matches that she is aware will be a formidable test.

"I have a bad record against Radwanska, I think I've never beaten her," laughed Pliskova afterwards. "It's going to be tough if I play her - but we didn't play for the last three years."

Diyas, meanwhile, can take comfort in a successful tournament that will boost her ranking back into the Top 50 for the first time since September 2015 - even more impressive given that this time last year, the 24-year-old was ranked No.209 and still recovering from wrist surgery.