Milos Raonic was forced to dig deep in his straight-sets win over Nicolas Mahut, while Grigor Dimitrov battled past Kyle Edmund at the ATP Citi Open.
Canadian third seed Raonic advanced to the round of 16 thanks to a 7-6 (7-2) 7-6 (8-6) victory in Washington on Wednesday.
Seeking his second Citi Open, Raonic - who reached the Wimbledon quarter-finals - saved two set points in the second set, converting his fourth match point after one hour, 56 minutes.
"There are a lot of things I need to be happy with," said Raonic. "I lost a bit of sharpness and discipline in the second set, but I'm glad I was able to get through and keep going in this tournament. It's good to be back, especially with that memory of having won here [in 2014]."
Raonic will next face Marcos Baghdatis, who upstaged 16th seed Ryan Harrison 6-4 6-1.
As for Dimitrov, the Bulgarian fourth seed prevailed 7-5 4-6 6-3 against Edmund in DC.
Dimitrov needed more than two hours to see off his British opponent, having only converted two of 10 break point opportunities.
German and fifth seed Alexander Zverev rallied to beat Jordan Thompson 4-6 6-3 7-6 (7-5).
Nick Kyrgios' return to the ATP circuit did not go according plan after he retired from his second-round clash with Tennys Sandgren.
In his first appearance since retiring at Wimbledon, 10th seed Kyrgios called time as he trailed 6-3 3-0.
Elsewhere, Gael Monfils was stunned 6-3 4-6 7-5 by qualifier Yuki Bhambri, Tommy Paul ousted seventh seed Lucas Pouille 7-6 (8-6) 6-3, Gilles Muller accounted for Dmitry Tursunov 6-1 6-2, Kevin Anderson saw off Malek Jaziri 6-4 6-1, Jared Donaldson dispatched Marc Polmans 6-2 6-3, while Daniil Medvedev shocked Steve Johnson 3-6 6-4 7-6 (7-1).