BASEL, Switzerland (AFP) - Second seed Alexander Zverev hammered a dozen aces to reach the semi-finals of the Swiss Indoors on Friday (Oct 26) with a 7-5, 6-3 defeat of Roberto Bautista Agut.

The win was a reversal of the first main draw match of Zverev's career when, as a 16-year-old wild card, he lost to Bautista Agut in Hamburg in 2013.

The 21-year-old German rallied from a break down in the second set to overhaul the Spaniard in one and three-quarter hours.

"He's a tough player with a dangerous game," the winner said as he prepared to face Romanian qualifier Marius Copil, who defeated Taylor Fritz 7-6 (8/6), 7-5.

Roger Federer was continuing the quest for his ninth hometown trophy later, taking on Frenchman Gilles Simon.

The Swiss top seed is playing in his 16th Basel quarter-finals, winning his last 14 in a row.

Zverev needed an hour to claim the opening set against Bautista Agut, reaching set point in the first with a backwards between-the-legs "tweener" which landed good.

In the second, he trailed, but was able to recover and complete victory, his 52nd of the season.

"(Trailing) 3-0 in the second, I started to play more aggressive. I was able to play my game," Zverev said.

"Copil has nothing to lose coming form qualifying, so I have to be ready for anything."

Zverev owns three titles this season, form Munich, Madrid and Washington.