Del Potro stunned, Isner through at Delray Beach

Juan Martin del Potro

Mackenzie McDonald upset top seed Juan Martin del Potro at the Delray Beach Open.

Juan Martin del Potro was stunned in the Delray Beach Open quarter-finals, while John Isner moved into the last four on Friday.

Del Potro’s first tournament back from a knee injury was ended by Mackenzie McDonald, who upset the Argentine top seed 6-4 3-6 7-6 (7-5).

The 2011 champion was unable to take either of his two break-point chances in the final set, edged by McDonald after two hours, 19 minutes.

McDonald will meet Radu Albot, who surprised fourth seed Steve Johnson 1-6 6-3 7-6 (7-5).

Isner made it seven wins in eight meetings with Adrian Mannarino thanks to a 7-6 (7-2) 6-4 victory.

The American will meet Dan Evans, the British qualifier having upset Italian sixth seed Andreas Seppi 6-4 6-4.

At the Rio Open, Pablo Cuevas remained on track to become the first man to win the ATP 500 event twice.

The Uruguayan 2016 champion overcame a second-set blip to get past Albert Ramos-Vinolas 6-3 3-6 6-3.

Awaiting him in the semi-finals is Felix Auger-Aliassime, the 18-year-old Canadian having claimed a 6-4 6-3 win over Jaume Munar.

The other last-four clash will be between Laslo Djere and Aljaz Bedene, who continued their runs.

Djere, who stunned Dominic Thiem in the first round, beat qualifier Casper Ruud 6-4 7-5.

Bedene eliminated third seed Marco Cecchinato in his opener and moved into the semi-finals courtesy of a 4-6 6-2 6-3 win over Hugo Dellien.