German Alexander Zverev has knocked Australian Sam Groth out of the Miami Open.

The 17-year-old Zverev won the first-round match 7-5 6-7 (5-7) 6-4 to send world No.69 Groth packing.

Earlier, Canadian Vasek Pospisil spoiled Juan Martin del Potro’s return from injury with a 6-4 7-6 (9-7) win over the 2009 US Open champion.

Argentina’s del Potro, a clear fan favorite, showed the rust after months of left wrist injury rehab in a contest lasting a shade under two hours.

The former world No.4, who has slumped to 616 in the rankings, double-faulted on a set point which would have levelled the contest at a set each.

Moments later he saved a match point with an ace, but finally succumbed with a service return long.

“I don’t feel frustrated, I have to take the positive things on my comeback,” del Potro said.

Del Potro, who had come back from right wrist surgery in 2010, underwent surgery on his left wrist last March.

He finished the 2014 season outside the top 100 for the first time since 2005 after contesting just four tournaments during the year.

Del Potro made an aborted comeback attempt in January before pulling out of the Australian Open because of pain in the wrist and underwent a second surgery two months ago.