Zheng Qinwen delivered an impressively dominant performance to defeat home hope Misaki Doi 6-2, 6-4 in 1 hour and 20 minutes in the first round of the Toray Pan Pacific Open.

In her most imperious passage of play, the Chinese 19-year-old reeled off 19 consecutive points -- the last three of the first set, and the first 16 of the second to build a 4-0 lead. No.107-ranked Doi battled hard to make the climax of the match more competitive, garnering one of the breaks back. However, Zheng served out the win at the second time of asking to set up a second-round clash against No.1 seed Paula Badosa.

Two former Top 20 players also enjoyed smooth passages into the second round. Petra Martic enjoyed Day 1's quickest win, needing only 69 minutes to defeat qualifier Rina Saigo 6-1, 6-1. No.635-ranked Saigo had been a qualifying wild card and was playing the first WTA main draw of her career.

Elsewhere, Elise Mertens made quick work of Wang Qiang, advancing 6-0, 6-3 in 1 hour and 22 minutes to take a 4-3 lead in their head-to-head. Mertens had lost their first three meetings in three sets, but has dropped only nine games in their most recent three clashes.

Mertens will next face Claire Liu, who defeated the only seed in action on Day 1, No.7 Alison Riske-Amritraj, 6-2, 6-3. The result was Liu's second career victory over a Top 30 player following her upset of Beatriz Haddad Maia in San Jose last month.

Highlights: Mertens d. Wang Qiang | Wang Xinyu d. Perez

Wang Xinyu won Monday's only three-setter, coming from a break down in the first and third sets to defeat qualifier Ellen Perez 7-5, 1-6, 6-4 in 2 hours and 4 minutes. It was just the Chinese 20-year-old's second win in nine matches since she was forced to withdraw from Wimbledon due to a thigh injury.

The final match of Day 1 saw Greece's Despina Papamichail triumph 6-4, 6-2 over China's You Xiaodi in a clash between qualifiers. Papamichail, 29, scored the first WTA main-draw victory of her career in Budapest this July, and this marked her first win at WTA 500 level. She will face No.3 seed Garbiñe Muguruza in the second round.