Mihajlovic selected a largely second-tier team in Sampdoria's 4-1 win over Verona on Thursday as the Genoa-based club qualified for the quarter-finals of the Coppa Italia.
Midfielders Bjarnason and Renan both scored, as did striker Gianluca Sansone, while the likes of defender Simon Poulsen and midfielder Enzo Maresca made rare starts.
Mihajlovic says he will have to think twice ahead of Sampdoria's clash with Catania on Sunday when he sits down to pick his team.
"We are on the right track (and) my applause to all the boys," the 44-year-old coach said.
"We must go on. We deserved to win and all the guys showed (commitment) and desire to do so.
"They put me in trouble for future choices."
For Renan, it was the Brazilian's second goal in as many games after he came off the bench to score the equaliser in Sampdoria's 1-1 draw away to Inter last week but Mihajlovic insisted the 27-year-old is far from the finished article.
"(Renan) needs to improve a lot and we're working on that," Mihajlovic said.
"I want midfielders who are not afraid to play and (take) two touches."
Sampdoria took control of the Coppa Italia clash early with Sansone and Bjarnason both scoring in the opening 20 minutes.
While Verona hit back after the hour-mark through Samuele Longo, Mihajlovic was thrilled with the way his side responded as substitute Nenad Krsticic and Renan struck in the final 10 minutes.
"I always want to see this spirit," the Serb said.
"Those who do not will have problems with me but I do not think (that) will happen."
