GSTAAD, Switzerland - Marketa Vondrousova became the first player into the quarterfinals at the Ladies Championship Gstaad with a 6-4, 6-4 victory over Elitsa Kostova.

The youngest active title-holder, Vondrousova lifted her first trophy in Biel/Bienne last April in just her second WTA main draw. Today's result is her first quarterfinal showing since then, although the 19-year-old did make the fourth round in Indian Wells this March.

Strong serving was the bedrock of the Czech's performance: winning 92% of rallies behind her first serve, Vondrousova would lose just 10 points behind her delivery throughout the match, two in the first set and eight in the second. Though she struck just two aces, the left-hander was rock-solid in her ability to construct points behind her serve, dictating effortlessly with her heavy forehand. The dropshot, too, was a key part of Vondrousova's strategy, and she would repeatedly use it to finish off longer rallies.

Elitsa Kostova reacts during her second-round loss to Marketa Vondrousova at the 2018 Ladies Championship Gstaad (Monika Majer/RvS Media)

This level of comfort on serve enabled the World No.104 to bide her time on return, holding back her full power while probing Kostova's game in their first career meeting. The Bulgarian, who had made the second round of a WTA tournament on seven occasions going back to 2014, was seeking to make her first quarterfinal at this level - and to that effect was ready to vary her approach over the course of the match.

Initially, the World No.186 would find success by sneaking into net, and an 84% first serve percentage would hold her opponent at bay in most of her service games. But on her sole break point opportunity in the first set, Vondrousova was sharp: upping the pace on her forehand, she seized her chance with an emphatic drive volley putaway.

Marketa Vondrousova celebrates during her win over Elitsa Kostova at the 2018 Ladies Championship Gstaad (Monika Majer/RvS Media)

Over the second set, Kostova was continually under the cosh. The 28-year-old had to save two break points in the first game and another two in a fifth game that featured the best tennis of the match from both players: a Vondrousova lob followed by an inside-out forehand rocket, an exquisite Kostova drop volley. By now, though, the teenager's own dropshots were becoming a touch predictable: Kostova clung on to several key points by chasing them down - and by beginning to deploy the tactic herself.

Nonetheless, having spent the first set rallying carefully, Vondrousova's increase in power paid dividends as she finally broke in the seventh game. A rare lapse into error on her own serve conceded the advantage - but a confident Vondrousova continued to outgun Kostova to break again and serve out to love, taking eight of the match's last nine points. In the quarterfinals, the former junior World No.1 will face either Mona Barthel or Evgeniya Rodina.