Coco Gauff won the battle of the American teenagers as she progressed into the San Diego Open second round with a 6-3 6-3 over Robin Montgomery on Wednesday.

The 2022 French Open finalist beat fellow 18-year-old Montgomery in a rain-affected match in one hour and 23 minutes, to clinch a last-16 clash with Bianca Andreescu.

The match marked Gauff's first game on tour since losing to Caroline Garcia in the US Open quarter-finals last month, although she had to endure an overnight rain delay, resuming on Wednesday up 6-3 3-2.

Gauff only needed 20 minutes on Wednesday to close out the victory, finishing the match with 3-0 aces, winning 76 per cent on her first serve and converting four of seven break points.

Croatian qualifier Donna Vekic continued her strong run with a 6-3 6-2 win over 2022 US Open quarter-finalist Karolina Pliskova. Vekic moved into the third round, having beaten Maria Sakkari in the first round too.

Fourth seed Jessica Pegula eased her way into the third round with a 6-3 6-1 victory over wild card Coco Vandeweghe in only 69 minutes. Pegula can secure her first WTA Finals qualification this week.

Danielle Collins was another American victor, triumphing 6-2 6-4 over Italy's Martina Trevisan in one hour and 27 minutes, reaching her third quarter-final of the year.