No.2 seed Anett Kontaveit extended her indoor winning streak to 17 in the second round of the St. Petersburg Ladies Trophy, defeating Sorana Cirstea 6-4, 7-5 in 1 hour and 31 minutes.

Last autumn, Kontaveit surged from No.30 to No.7 in the space of two months - in large part due to racking up three indoor hardcourt titles in Ostrava, Moscow and Cluj-Napoca. In St. Petersburg this week, the Estonian is again demonstrating how these conditions suit her big-hitting game.

Against Cirstea, she needed to recover from a break down in the second set, but ultimately maintained her mastery over the Romanian. Kontaveit has now won all six of their meetings dating back to 2016, including a trio of victories last year, and dropped just one set in total.

Match management: Kontaveit's game may thrive indoors, but even more important was her ability to play the big points like the Top 10 player she has recently become. In a high-quality shotmaking encounter that was tighter than Kontaveit's head-to-head dominance suggests, Cirstea played stellar tennis to repeatedly give herself opportunities. Taking those opportunities was not as simple, though.

In the first set, Cirstea missed three break point opportunities in the third game and fell down a break for 4-2, but fired a brace of breathtaking returns to level at 4-4. A marvellous pass took her to deuce on the Kontaveit serve in the next game, but the World No.9 found her biggest deliveries to extricate herself from danger.

The first half of the second set saw Cirstea coming out on top of more of the longer and higher-quality exchanges, and she was rewarded with a break for 4-3. But Kontaveit swiftly erased the deficit thanks to some ferocious returning of her own, then took the best point of the match - turning scrambling defence into emphatic offence - to hold for 5-4.

Serving to stay in the match at 5-6, Cirstea's resistance collapsed. The World No.31 coughed up two cheap unforced errors and a double fault, and Kontaveit took full advantage to seal victory with a powerful off forehand.

What's next for Kontaveit: The 26-year-old's streak will be tested in the quarterfinals against either No.5 seed Belinda Bencic or qualifier Kaja Juvan.

Mertens comes through battle over Martic; Rybakina dominant in opener

Like Kontaveit, No.8 seed Elise Mertens also preserved a perfect head-to-head to book her place in the quarterfinals. Her 6-4, 3-6, 6-2 defeat of Petra Martic was her third in as many meetings with the Croat, but the first which had gone to three sets.

There were two key momentum swings in the match. Mertens' backhand was on song in the initial stages, and she raced out to a 5-1 lead. But after Martic saved three set points in that game, the World No.70 began to show off her full repertoire of slices, dropshots and volleys.

Martic controlled the middle section of the match, winning 10 out of 14 games. It wasn't enough to rescue the first set - though she cut Mertens' lead to 5-4, an ill-advised net rush enabled the Belgian to pass her and seal a fifth set point. But Martic raised her first serve percentage from 47% to 69% in the second set, capturing the key break for 4-2 with marvellous all-court point construction.

After a perfectly weighted dropshot sealed an immediate break in the third set, Martic seemed to be in the driver's seat. But a poorly executed one in the next game was a gift for Mertens to swat away, and from there the World No.26 resumed her initial form.

Tightening up her serve, which had been afflicted by ill-timed double faults in the second set, Mertens grew in confidence. By contrast, Martic faded; serving to stay in the match, she netted a smash, a forehand, a backhand and finally a volley.

Highlights: Mertens d. Martic | Rybakina d. Gracheva

Earlier, No.3 seed Elena Rybakina completed first-round action with a 6-2, 6-1 defeat of qualifier Varvara Gracheva in just 57 minutes.

The 2020 finalist had started this season brightly with a runner-up showing in Adelaide, but was forced to withdraw from Sydney and retire in the second round of the Australian Open due to a thigh injury. Rybakina showed no sign of that ailment as she overpowered Gracheva, though. The Kazakh lost only one point behind her first serve, and did not face a break point over the course of the match.