In just her second appearance at the Dubai Duty Free Tennis Championships, Madison Keys advanced to the third round with a 7-5, 6-4 win over No.4 seed Caroline Garcia.

On paper, the result was an upset. No.23-ranked Keys captured the 11th Top 5 win of her career, and the first since her defeat of World No.1 Iga Swiatek in Cincinnati last year.

But it was in keeping with the pair's history. Keys has now won four straight matches against Garcia. Since the Frenchwoman won their first meeting in 2014 Billie Jean King Cup action, Keys has not lost a set to her.

The former US Open finalist Keys will next face No.15 seed Victoria Azarenka. She has yet to defeat Azarenka in four previous meetings, including a 1-6, 6-2, 6-1 loss in the third round of the Australian Open last month.

Azarenka, the runner-up in Dubai back in 2010 to Venus Williams, overcame Amanda Anisimova 4-6, 6-4, 7-6(5) after coming from 5-3 down in the third set.

Highlights: Azarenka d. Anisimova

Elsewhere, 20-year-old Zheng Qinwen was forced to withdraw from her second-round match with No.14 seed Liudmila Samsonova due to abdominal pain. Samsonova, the Abu Dhabi runner-up two weeks ago, advances via walkover and face either No.1 seed Iga Swiatek or Leylah Fernandez.

How the match was won: With both players deploying an aggressive approach, rallies were in short supply and the serve was pre-eminent. Keys ultimately led in every category: a better first serve percentage (60% to 50%), more points won behind both first and second serve, more winners (19 to 13) and fewer unforced errors (34 to 46).

Underneath the numbers, Keys was also more astute in controlling her game on the most important points. She picked the right moments to unleash on return and came to net judiciously. Toward the end, she also found success with higher-margin backhand winners behind Garcia.

By contrast, Garcia opted for increasingly extreme forms of offense when the match got tight. She was beset by seven double faults, including three on the penultimate point of each game in which she lost serve. In the final game, she also handed Keys a match point after charging forwards off the return and missing the attempted volley.

Pegula comes through seesaw battle: Keys' American compatriot and United Cup teammate Jessica Pegula joined her in the last 16 after defeating qualifier Viktoriya Tomova 6-2, 5-7, 6-1.

No.3 seed Pegula, fresh off a run to the Doha final last week, did not have it all her own way against the World No.99. After a one-sided first set, Tomova's off-pace changes of direction and creative shot selection began to have an impact, eliciting uncharacteristic errors from the Pegula racquet.

More Dubai second-round highlights: Pegula d. Tomova | Muchova d. Cirstea | Kvitova d. Putintseva

During an absorbing second set, a run of six out of seven games all went to deuce as Tomova built a 5-1 lead, only for Pegula to inch her way to levelling at 5-5. During this passage of play, six set points came and went for the Bulgarian -- though only the forehand sitter she missed on the second was cause for regret, as Pegula found solid winning shots to fend off the rest.

Pegula held a point to lead 6-5 -- only for Tomova to produce a brilliant return winner, and go on to break again herself. At the third time of asking, Tomova closed out the set, converting her seventh set point with a service winner.

But all the momentum Pegula had built up was not in vain. The five-time Grand Slam quarterfinalist delivered a watertight third set in much the same vein as the first, rattling through six of the last seven games to set a third-round clash with either Shelby Rogers or Ana Bogdan.