Florian Mayer and Nikolay Davydenko recorded straight-set victories at the Open Sud de France in Montpellier.
Number three seed Mayer defeated Luxembourg's Gilles Muller 7-6 (7-3) 6-3 in their first-round clash at Arena Montpellier.
German Mayer saved all seven of the break points he faced to advance in one hour and 20 minutes.
Davydenko snapped a four-match losing streak with a comfortable 6-2 6-1 win over Stephane Robert.
The Russian's last win came in Valencia in November, but he ended his drought in emphatic style, progressing in under an hour.
French wild card Guillaume Rufin edged out Vasek Pospisil of Canada 6-4 7-6 (8-6) in the day's other match.
Meanwhile, seeds Ivan Ljubicic and Andreas Seppi recorded contrasting wins on the opening day at the Zagreb Indoors.
Local hope Ljubicic, the top seed at the ATP 250 event, edged Karol Beck of Slovakia 7-6 (7-5) 3-6 6-3 in two hours and 18 minutes.
The Croat served 16 aces for the match, staying on track to reclaim the title he won in 2006.
Fifth seed Seppi secured a more comfortable passage into the second round, defeating Daniel Brands 6-4 7-6 (7-1).
Italian Seppi won 70 percent of his service points and claimed victory after one hour and 28 minutes.
Also, seventh seed Robin Haase eased past wild card Kristijan Mesaros 6-2 6-3, while German Matthias Bachinger accounted for South African Izak van der Merwe with a 6-3 6-3 win.
And Slovakian Lukas Lacko had to battle before overcoming Italy's Potito Starace, earning a 7-6 (7-2) 6-7 (4-7) 6-3 victory in two hours and 13 minutes.
In Chile, the opening round of the VTR Open served up a pair of shocks as seeds Santiago Giraldo and Filippo Volandri both lost.
Colombian Giraldo, a beaten finalist at the ATP 250 event last year, suffered a 6-7 (5-7) 1-6 reverse to Argentine Leonardo Mayer.
In another first-round upset, Brazil's Joao Souza defeated number eight seed Volandri, edging the Italian 1-6 7-5 7-6 (7-5) in two hours and 53 minutes.
The main draw was completed after Rogerio Dutra Silva, Diego Junqueira, Ruben Ramirez Hidalgo and Federico Delbonis won their qualifiers.