Petkovic started Floccari, Keita, Mickael Ciani and Ogenyi Onazi in Lazio's 1-0 triumph over Legia in the UEFA Europa League on Thursday with the likes of regular starters Cristian Ledesma, Senad Lulic and Miroslav Klose rested on the bench.
Thursday's clash was Lazio's first game of seven in the space of three weeks and Petkovic was thrilled with how his lesser lights got the job done against their Polish opponents.
"The positive competition among players is very useful when you have to play seven matches in 21 days," Petkovic said after the win.
"It's important to have all players at top conditions.
"For this match we managed to make a very specific work and this is very useful, especially for the players playing in the national teams, so that they can have a break but also work in the right way, recover energy and get ready for the forthcoming matches."
Lazio's next match will be against fellow capital club Roma in Italy's Serie A and Petkovic claimed his team's win over Legia will help heading into Sunday's derby.
"Tonight we made a good performance and this victory allows us to face the forthcoming matches more calmly," the 50-year-old Bosnian said.
"Now we should recover our energy even if there isn't much time to get ready for the next match, but I'm sure the guys will do their best to win the match against Roma."
Lazio sit seventh on the Serie A table with two wins from three games so far this season, while Roma are second with a perfect record, three points ahead of their arch-rivals.
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