Defending champion and top seed Andrey Rublev has eased into the St. Petersburg Open quarter-finals with a straight-sets victory over Ilya Ivashka.

World No.6 Rublev was on court for one hour and 30 minutes before he clinched the last-16 match 6-4 6-4.

His fellow Russian Karen Khachanov was victorious 6-3 6-3 over Adrian Mannarino in their opening round encounter, after a typically solid service match in which he did not face a single break point.

In the second round of the ATP Tour 250 event, the sixth-seeded Khachanov will face Croatian veteran Marin Cilic, who saw off Albert Ramos-Vinolas 6-2 6-3.

Canadian Denis Shapovalov, who has a Russian father and is seeded second, had to recover from losing the first set to Pablo Andujar to join Rublev in the quarter-finals with a 2-6 6-3 6-0 success.

German Jan-Lennard Struff provided the day's upset by accounting for Alexander Bublik, the seventh seed, 6-4 6-3 to also reach the last eight.