Australia’s Sam Groth has pulled off a shock second-round win, claiming the scalp of world number 14 Feliciano Lopez to storm into the Mercedes Open quarter-finals in Stuttgart.

In a three-set showdown, the 27-year-old from Melbourne, who is ranked 66th in the world, dug deep to claim a 3-6, 7-6 (7/5), 7-6 (8/6) win over the Spaniard, in just over two hours on Wednesday.

Groth’s big serve helped him recover from losing the first set, to eventually take down Lopez and set-up a quarter-final clash with eighth seed Viktor Troicki.

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“Grass court is probably my favourite surface,” Groth said post-match.

“I had a pretty good season last year on it, it’s definitely a surface I’m comfortable on and I’ve had seven good matches now.

“I feel like I’m finally making some big steps.”

Troicki is returning from a six-month ban for failing to provide a blood sample.

The 29-year-old saw off 18-year-old German Alexander Zverev, the youngest player in the top 100, 6-3, 6-7 (6/8), 6-3.

– with AAP