Alexandr Dolgopolov failed to build on his Citi Open success as he was dumped out of the Rogers Cup in Toronto.
Dolgopolov had beaten Tommy Haas on Sunday to clinch his second ATP World Tour title - but he managed to win just four games as he was brushed aside by Radek Stepanek.
Stepanek won 85% of points on his first serve, breaking his Ukrainian opponent - the world No. 16 - four times as he cruised to a 6-3 6-1 victory in just 65 minute.
The 33-year-old from Czech Republic will now face Olympic bronze medallist Juan Martin del Potro in the second round.
Haas fared better than his Washington conqueror in his first-round match, responding from the disappointment of passing up four match-points in the second-set tie-break to defeat David Nalbandian 6-2 6-7 (11/13) 6-3.
Americans Mardy Fish and Sam Querrey advanced with straight-sets wins. Fish, the 11th seed, crushed Matthew Ebden 6-2 6-0, while Querrey dropped only nine points on serve en route to a 6-3 6-2 triumph over Jurgen Melzer.
Milos Raonic, the 16th seed, was in second-round action and progressed after a 6-3 6-4 success against Viktor Troicki.
Vasek Pospisil missed out on a place in the last 16, though, going down 7-5 6-4 against seventh-seeded Juan Monaco.
Also in the second round, eighth seed John Isner overcame Pablo Andujar 7-6 (7/5) 7-5 in the late match.
In other first-round encounters on Tuesday there were wins for Mikhail Youzhny, Marcel Granollers, Fabio Fognini, Julien Benneteau and Mikhail Kukushkin.
