Defending champion Novak Djokovic silenced concerns about his left shoulder as the Serbian breezed past American Denis Kudla 6-3 6-4 6-2 on Friday to reach the last 16 at the US Open.
Djokovic's title defence looked to be in jeopardy in his previous match when he received treatment on his shoulder several times, an issue which he said had impacted his serve and backhand.
But he looked to be playing pain free against Kudla, the 16-times Grand Slam champion winning 81% of his first-serve points and turning aside all seven break points he faced against the unseeded American.
"I managed to play almost pain free, that's a big improvement from my last match," said top seed Djokovic.
"Obviously I didn't know how the body would react and I am just glad to finish the match tonight."
Kudla, who due to a rain delay earlier this week was playing his second match in as many days, brought incredible energy into the match and raced around the court to make a number of shots that surprised Djokovic but was simply overmatched.
Djokovic came out firing right from the start as served out to love to begin the match and broke Kudla for a 3-1 cushion en route to wrapping up the first set without showing any signs of distress.
The Serb broke again in the fifth game of second set and was in total control as he served out to love in the ensuing game for a 4-2 cushion.
Djokovic opened the final set with another break and added another in the seventh game before closing out the match when he served out to love.
Up next for Djokovic will be former champion Stan Wawrinka, who fought off a spirited challenge from Italian Paolo Lorenzi 6-4 7-6(9) 7-6(4) earlier on Friday.
Djokovic owns a 19-5 career record versus Wawrinka, who is seeded 23rd, but has not faced the Swiss since losing to him in the 2016 US Open final.
After slow starts in his first two US Open matches, Roger Federer took his game up a notch with a stress-free 6-2 6-2 6-1 win over Briton Daniel Evans to reach the round of 16.
Serena cruises into fourth round
Serena Williams moved another step closer to a record-tying 24th career Grand Slam title with a comfortable 6-3 6-2 victory over Czech Karolina Muchova this morning to reach the last 16 at the US Open.
Wimbledon quarter-finalist Muchova held serve for an early 3-2 lead in her first career meeting with Williams but the six-times champion cranked up the pace and won the next seven games to take over the match.
Williams took advantage of a poor serving performance by Muchova and broke her opponent five times, including in the final game where she sealed the victory with when the Czech sent a backhand long.
Up next for Williams will be Croatian 22nd seed Petra Martic.
Ashleigh Barty has passed the sternest test yet of her US Open title credentials to equal her best-ever run in New York.
Australia's world No. 2 delivered a serving masterclass class to reach the last 16 for the second straight year with a composed 7-5 6-3 victory over rising Greek Maria Sakkari.
Third-seeded Karolina Pliskova advanced to the round of 16, downing Ons Jabeur 6-1 4-6 6-4.
Pliskova, a former world No.1 who reached the final at Flushing Meadows in 2016, won despite looking out of sync for much of the match.
Earlier, American qualifier Taylor Townsend took a nothing-to-lose attitude into her clash with Simona Halep to pull off the upset of the week.
Her aggressive approach frustrated the Romanian fourth seed and secured her first career win over a top 10 player.
Crowd-pleasing teenager Coco Gauff came through a tough battle with qualifier Timea Babos 6-2 4-6 6-4 to set up a third-round clash against top seed and defending champion Naomi Osaka.
The 15-year-old American phenom was forced to dig deep to become the youngest player since Anna Kournikova in 1996 to reach the third round of the women's singles at Flushing Meadows.
Two Kiwis out in first round
New Zealand men's doubles player Marcus Daniell and his British partner Ken Skupski have lost their US Open first round match to Australian Nick Kyrgios and Romanian Marius Copil 7-6 5-7 7-5.
Daniell and his partner won the first set tiebreaker. Kyrgios and Copil then took the second set 7-5.
The third set went to another tie-breaker but big serving Kyrgios sealed it with an ace.
Also this morning, New Zealand doubles player Michael Venus and his South African partner Raven Klaasen beat the difficult French combination of Adrian Mannarino and Gilles Simon 6-2 6-1 in the first round.
Fellow compatriot Artem Sitak and his partner lost 6-2 6-4 to second seeds Lukasz Kubot and Marcelo Melo.