New York - Serena Williams will be aiming to step it up against Vania King on Thursday as she eyes a third-round spot in the US Open, where Andy Murray seeks to move closer to a second Grand Slam title of the season.
World number one Williams, who matched the Open Era record for Grand Slam titles with her 22nd at Wimbledon, said she had plenty of room for improvement after a 6-3, 6-3 first-round win over Ekterina Makarova.
"I think I can get a lot better," said the US superstar, who fired 12 aces and 27 winners against the Russian lefty - and said she'd have to wait and see if the work reignited the painful inflammation in her right shoulder.
Even if it does flare up, Williams has to be considered a strong favourite against her 87th-ranked compatriot King, a wild card she trounced 6-1, 6-0 in their only prior meeting, in the second round of the 2014 US Open.
Murray, fresh off Wimbledon and Rio Olympic triumphs and trying to become the fourth man to reach all four Grand Slam finals in a calendar year, has a longer history against Spain's Marcel Granollers.
But the Scot can go in with confidence having won six of their seven encounters - the most recent at the Indian Wells hard-court Masters in March.
Murray was delighted to get past tough Czech Lukas Rosol in straight sets in the first round, sparing himself an ultra-late night on Tuesday.
On Thursday he'll face the different conditions of an afternoon match - with predicted scattered showers making it possible the new roof on the Arthur Ashe stadium court could be called into action, after being closed for the first time during light rain on Wednesday night.
If so, Murray will be ready.
"I think it's great," Murray said of the $150 million retractable roof, which he practiced under before the tournament kicked off.
"It's very quick too to open and close. Shouldn't be too many delays. For players it's a good thing."
Other marquee players eyeing a place in the last 32 on Thursday include Serena's elder sister Venus, the sixth, seed, who takes on German Julia Goerges.
Women's fourth seed Agnieszka Radwanska of Poland takes on Briton Naomi Broady and fifth-seeded Romanian Simona Halep plays Czech Lucie Safarova.
Men's third seed Stan Wawrinka of Switzerland faces Italian qualifier Alessandro Giannessi in the first meeting between the two.
Sixth-seeded Kei Nishikori of Japan and eighth-seeded Dominic Thiem of Austria also face unfamiliar foes, Nishikori against Russian qualifier Karen Khachanov and Thiem against Lithuanian Ricardas Berankis.