Second seed Kei Nishikori came from a set down to beat Australia's James Duckworth and reach the third round of the Citi Open in Washington.
Duckworth saved a set point to win the first set in a tie break but the Japanese player surged back to win 6-7 (8/10) 6-1 6-4.
Sam Querrey also needed three sets, beating Nishikori's compatriot Go Soeda 6-3 5-7 6-4, but the remaining seeds in action made routine progress.
Third seed Marin Cilic was the day's final winner, 7-6 (7/2) 6-3 against South Korea's Hyeon Chung, while Vasek Pospisil (12) beat Donald Young 7-5 6-3 and Jack Sock (15) won 7-6 (9/7) 6-3 against Belgian Ruben Bemelmans.
Lleyton Hewitt beat fellow Australian John-Patrick Smith 6-3 6-4 while Sam Groth battled to a 7-6 (10/8) 4-6 6-3 win over Brazilian Thomaz Bellucci.
Alexandr Dolgopolov won 6-4 6-2 against American Tim Smyczek and there were also wins for Gilles Muller, Steve Johnson, Guido Pella and Blaz Rola.
The only seed to fall in either the men's or women's draw was CoCo Vandeweghe, the seventh seed losing to her fellow American Christina McHale 6-2 4-6 6-4.
The top four seeds were all in action, headed by Ekaterina Makarova - the Russian won 7-5 7-5 against Belgium's Alison van Uytvanck.
Sam Stosur was presented with a cake to mark her 500th win on the WTA Tour, a 6-2 6-2 dismissal of France's Kristina Mladenovic, while Belinda Bencic beat Tereza Smitkova 7-5 6-4 and Svetlana Kuznetsova saw off home qualifier Sanaz Marand 6-2 6-4.
Sloane Stephens brushed aside Magda Linette 6-2 6-1, while Anastasia Pavlyuchenkova needed two tie-breaks to get past Magdalena Rybarikova.
Great Britain's Naomi Broady battled from a set down and also saved a match point in the final-set tie-break as she earned an impressive 3-6 7-5 7-6 (8/6) success against Australian Jarmila Gajdosova.
Slovenia's Polona Hercog won 6-2 7-5 against Israeli qualifier Julia Glushko.
Source: PA
