At the European Open in Antwerp, Jo-Wilfried Tsonga began his campaign victory with a thumping victory over Lorenzo Sonego.
The 2017 champion and sixth seed - aiming to win his third title of the season - recorded a break of serve in each set to go through 6-3 6-4, with either fellow Frenchman Gilles Simon or Belgian Steve Darcis up next for Tsonga.
Life was far tougher for fifth seed Guido Pella on Monday, however, as he fought back from a set down to beat German Peter Gojowczyk 5-7 6-4 7-6 (7-2).
At the Stockholm Open, Janko Tipsarevic kicked off his final tournament on the ATP Tour in fine style, beating Corentin Moutet 6-2 6-4 in just 73 minutes.
The 35-year-old has announced he will retire after the Davis Cup Finals in November, though his singles career is not finished just yet. Next up for Tipsarevic is the top seed this week in Sweden, Italian Fabio Fognini.
Dan Evans won 6-4 1-6 6-3 against Bernard Tomic but fellow seed Reilly Opelka was on the wrong end of an upset, losing a three-set battle to Stefano Travaglia 7-5 4-6 6-4.
There was also a surprise in the opening round of the Kremlin Cup in Moscow, with Andreas Seppi eliminating fifth seed Cristian Garin 3-6 7-6 (7-2) 7-6 (7-4). In contrast, Adrian Mannarino, the seventh seed, breezed by qualifier Damir Dzumhur 7-6 (7-2) 6-0.