Defending champion beat German Philipp Kohlschreiber in two hours and two minutes on Monday to reach the second round.
Novak began his quest for a first Roland Garros crown with a 6-2, 7-5, 6-2 victory over 87th-ranked Jarkko Nieminen on Tuesday.
Novak and Viktor both won on the opening day at Kraljevo Sports Centre to give Serbia a 2-0 lead over Croatia going into Saturday’s doubles.
Kraljevo, Day 1: 13.00 CET Novak Djokovic (SRB) vs Mate Delic (CRO), followed by Viktor Troicki (SRB) vs Borna Coric (CRO).
The top seed opened his bid for a fifth Dubai Duty Free Tennis Championships title with a 6-4, 6-4 victory over Vasek Pospisil on Tuesday.
World no.1 opened his Australian Open campaign with a 6-3, 6-2, 6-4 win over qualifier from Slovenia Aljaz Bedene (116) on Tuesday.
Novak successfully started his 2015 season in singles on Tuesday with a convincing 6-2, 6-1 win over Dusan Lajovic at the Qatar ExxonMobil Open.
Nole moved to 20-0 at the China Open with a 6-2 6-1 win over Spaniard Guillermo Garcia-Lopez on Tuesday.
The top seed closed out a routine 6-1, 6-2, 6-4 win over world no.79 Diego Schwartzman to advance into the second round of the 2014 US Open on Monday night.
Novak and Stan beat Cabal/Marrero 6-3, 7-5 to advance into second round of doubles competition at the Rogers Cup in Toronto.