ZHUHAI, China -- Zheng Saisai thrilled her homeland crowd in the last round-robin match of Day 1 at the Hengqin Life WTA Elite Trophy Zhuhai, as she upset No.3 seed Madison Keys of the United States, 6-4, 6-2.

"I am pretty happy about the win today because I didn't expect to win today," Zheng admitted, after the match. "I was just going to fight for it."

World No.40 Zheng, the wildcard into the 12-woman field, claimed victory over Keys after 91 minutes of play. The upset win avenged a straight-set loss to the 13th-ranked American in their only previous clash, which also took place in the round-robin portion of Zhuhai in 2015.

"I think I played pretty solid today," said Zheng. "[Keys] didn't put many first serves in, which gave me more opportunities to go into the rallies and start to run her. So I think that's the key for today."

"When I served, I tried to just surprise her," Zheng continued. "I mixed up a lot, like I'm not going only wide or only to the T, she didn't know where I was going to serve. So I think I am doing pretty consistent today."

The strong season for Chinese No.2 Zheng continues unabated. Zheng claimed her first-ever WTA singles title at San Jose this summer, propelling her to a career-high ranking of No.37 in August. Her win over Keys is her third victory over a Top 20 player this season.

Zheng started the match off well, using dropshots to great effect and reaching break point in the first game, then forcing an error with her backhand to take the early lead. Keys, however, struck right back for 1-1, converting her third break point of the game with a winning volley.

Both players were already trying to polish off points in the forecourt whenever they could, but it was Keys who found herself in peril on serve more often than her opponent at the outset of the encounter. The American had to save three more break points before holding for 2-1, and then was broken by Zheng in her next service game as the hometown heroine forced errors from the American.

Once again, Keys quickly got back to level terms, punching another volley winner on break point to reach 3-3. The American, though, was never quite able to keep her momentum rolling after breaking serve, and Zheng swiftly garnered a break point in the very next game with a stirring forehand pass down the line. Zheng subsequently fired another forehand to break again and move ahead 4-3.

This time around, Zheng would not cede her advantage, and she continued to use her variety to the best of her ability, carving her way to 5-3 with dropshots and volleys. Zheng had to face a break point when serving for the set at 5-4, but she fended Keys off with a well-timed strong serve, and closed out the opener on her second set point after a wide backhand from the American.

Zheng immediately established dominance in the second set after outlasting Keys in a rally on break point in the first game. The Chinese player rolled on from there, breaking Keys twice more en route to a commanding 5-0 lead. Keys got one break back as she edged to 5-2, but was still in a dire predicament as she faced Zheng serving for the match for a second time.

Keys pulled from 30-0 to 30-30 in that game, but netted a backhand to queue up Zheng’s first match point. A forehand winner by the American brought the game to deuce, but a netted return gave Zheng a second chance. There, Zheng prolonged a rally with outstanding defense before closing out the lengthy point, and the match, with a forehand winner down the line.

Zheng now finds herself in great standing in the Orchid Group, with a victory over the three-woman group’s top-ranked player. World No.15 Petra Martic also resides in the Orchid Group with Zheng and Keys, as the trio will battle each other for one semifinal spot.