Saint Petersburg - German teenager Alexander Zverev, ranked 27th in the world, on Monday cruised into the second round of the St Petersburg Open with a straight-set win over Russian wildcard Karen Khachanov.
The 19-year-old fifth seed won his first ever meeting with Khachanov 7-6 (7/3), 6-4, as he targets his maiden ATP title.
The German took the opening set in a tiebreak after 47 minutes before fighting back from 3-0 down in the second set to close out the match in one hour 25 minutes.
The Monte Carlo resident will now face the winner of the clash between Russians Daniil Medvedev and Alexander Bublik for a place in the last eight.
"I was really nervous at the beginning as I didn't play for three weeks after the US Open," Zverev said.
"Luckily, I then managed to find my rhythm and everything went fine for me."
Earlier, Ricardas Berankis of Lithuania, 83rd in the ATP rankings, ousted Frenchman Adrian Mannarino 7-6 (9/7), 3-6, 6-3 to set up a meeting with fourth seeded Spaniard Roberto Bautista Agut.
Mannarino produced a catalogue of errors from the start but forced his way back from a break down to force a tiebreak, which the 26-year-old Lithuanian won.
In the second Berankis was 2-0 up with an early break but Mannarino broke back twice to level at one set all.
The opponents traded breaks throughout the deciding set but Berankis edged it to claim the set and the match in two hours six minutes.
"It wasn't that easy as my opponent performed a variety of shots making it difficult for me," Berankis said.
"We were both up and down today but at the end I was a bit more lucky."
Lukas Rosol of the Czech Republic dropped serve twice but broke Argentina's Diego Schwartzman on five occasions in a 6-4, 6-4 win in 80 minutes.
The 31-year-old will now meet top-seeded Swiss Stan Wawrinka, the freshly crowned US Open champion who enjoyed an opening-round bye.