Del Potro wins through to Delray Beach Open quarter-finals

Del Potro returned from wrist injuries and to the court for the first time in almost 11 months as he beat Denis Kudla in straight sets on Tuesday.

And the Argentinean continued where he left off, seeing off his Australian opponent to reach the quarter-finals.

Del Potro broke Smith to 15 to close out the match in an hour, 17 minutes at the ATP 250 tournament.

Awaiting Del Potro in the last eight is good friend and fifth-seeded Frenchman Jeremy Chardy.

Chardy booked his spot in the quarter-finals with a 6-4 6-2 win over American Noah Rubin.

Despite serving at just 49 per cent, Chardy fired down six aces, converted five break points and saved four of his own to move a step closer to his first semi-final since the Rogers Cup in August last year.

"I know [Del Potro] really well," Chardy said. "He's one year younger than me so we've known each other since we were kids. He's a good friend of mine. We had a lot of fun in juniors together. We never missed a players' party [back then].

"I was really happy for him to come back. For a tennis player, the worst is to be injured. [His comeback] is great for the fans too. We need players like him on the tour."

While Chardy advanced, seventh seed Donald Young was a shock second-round casualty.

Young lost out to fellow American Tim Smyczek, who rallied to a 1-6 7-6 (7-2) 6-2 victory.

Smyczek came from a break down in the second set to reach his second quarter-final on the ATP World Tour.

Next up for Smyczek is compatriot Sam Querrey, who accounted for Austin Krajicek 6-4 6-3 in an all-American affair.