ST. PETERSBURG, Russia — Stan Wawrinka kept his injury comeback on track with a hard-fought win over Karen Khachanov to reach the quarterfinals of the St. Petersburg Open on Wednesday.

Wawrinka saved two set points in each set on his way to winning 7-6 (10), 7-6 (1) over the fourth-seeded Khachanov, who at No. 24 is ranked 64 places above Wawrinka.

Wawrinka's quarterfinal opponent will be either defending champion Damir Dzumhur or Guido Pella.

Second-seeded Fabio Fognini's tournament ended quickly as the Italian lost his opening match 6-3, 6-4 to Martin Klizan in 1 hour, 15 minutes.

Also Wednesday, fifth-seeded Roberto Bautista Agut beat qualifier Luca Vanni 7-5, 6-2 in their first-round match.

Canadian 19-year-old Denis Shapovalov, seeded seventh, won 7-6 (3), 6-2 against qualifier Adrian Menendez-Maceiras. He'll meet Matteo Berrettini of Italy in the second round for the opportunity to play Klizan in the quarterfinals.

Playing his last tournament before retirement, Russian veteran Mikhail Youzhny prolonged his career by at least one more match with a 7-6 (6), 6-4 win over Mirza Basic.

Youzhny, a former top-10 player with 10 tour titles to his name, goes on to meet Bautista Agut in the second round.