Andrey Rublev celebrated a top 10 ranking by beating Canada’s Vasek Pospisil 6-2 6-4 in St Petersburg.
Rublev converted 4 of his 13 break points and saved three of the four break points he faced and won 87 per cent of first serve points.
Milos Raonic hit 21 aces and saved all five break points to beat US qualifier JJ Wolf 7-6 (7-5) 6-1.
Borna Coric beat Spanish veteran Feliciano Lopez 6-3 7-6 and Miomir Kecmanovic came back from 3-6 down in the second set of the tie-break of the second set and saved three set points to beat Mikhail Kukushkin 6-3 7-6 (9-7).
The Serb set up a second round match against Cameron Norrie, who beat Taylor Fritz 6-4 4-6 6-3 on Monday.