Top seed Juan Martin del Potro has maintained his push for a place at the season-ending ATP Tour finals in London with a first-round victory at the China Open in Beijing.
Playing his first match since last month's US Open final, the popular Argentine beat Spain's Albert Ramos-Vinolas 7-5 6-2 in just under one-and-a-half hours on Tuesday.
But it was not without a struggle for 30-year-old Del Potro, who must reach the final in China to book his finals for the first time since 2013, as he received on-court treatment for a twisted knee during the first set.
He will play Russia's Karen Khachanov in the second round.
Second-seed German Alexander Zverev stepped up his push to qualify for the elite London field as he beat Spaniard, Roberto Bautista Agut 6-4 6-4.
Rafael Nadal, Roger Federer and Novak Djokovic are the three players to have secured their places in the season-ending tournament.
Bulgarian third seed Grigor Dimitrov, a finalist in Beijing two years ago, began his campaign with a solid 7-5 6-3 victory over American Tennys Sandgren.
"It's never easy when you've never played against a guy," Dimitrov, whowill next face Serbian Dusan Lajovic.
"So it took me quite a few games to kind of get in a rhythm, see what kind of game plan he had (and) just try to get comfortable in the match."
Spain's Fernando Verdasco was made to work for two hours and 23 minutes before he overcame France's Gael Monfils 2-6 7-6 (7-3) 7-6 (7-5) in a battle of former top-10 players.
Fourth-seeded Italian Fabio Fognini maintained his faint hopes of reaching London with a 1-6 6-3 6-3 victory over qualifier Radu Albot.
Other first-round winners in Beijing on Tuesday were Italian eight seed Marco Cecchinato, Nikoloz Basilashvili, who upset sixth-seeded American Jack Sock, Andrey Rublev, Filip Krajinovic and qualifier Matteo Berrettini.
