The Eagles were presented with another opening soon after as Mitrovic's deflected strike from inside the box was comfortably gathered by Keylor Navas, before a quiet spell ensued.
Here are five things we learned from the first game of Group E.
Cristiano Ronaldo's sensational display against Spain on Friday night has been the performance of the 2018 World Cup so far, with Brian Kerr's commentary a close second.
Taking over as full-time Serbia coach in December 2017, Krstajić was taking charge of his first competitive game as manager both of Serbia and in general.
And the 44-year-old could not have dreamed for a better start as his side beat Costa Rica 1-0 in what may prove to be an important match in Group E, with many expecting Brazil to win the group and the other three (Serbia, Costa Rica and Switzerland) playing for second place.
Costa Rica defender Ronald Matarrita was ruled out of the World Cup earlier this week because of a right hamstring injury.
But four years on, Los Ticos looked uninspiring in Russian Federation as Serbia pushed to to a straight-forward 1-0 win.
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While the president remained mum on the report's findings, White House press secretary Sarah Sanders offered the first reaction. Trump and his supporters have repeatedly claimed Clinton should have faced further consequences.
After Mitrovic was fouled, Kolarov stepped up to the free-kick, all of 30 yards from goal, and struck it an inch inside the post, leaving even a keeper of Navas' quality grasping at thin air. "The match against Switzerland is going to be the most hard one".
Sergej Milinković-Savić, the Lazio midfielder who could be in the middle of this summer transfer window's biggest tug of war, nearly provided it.
Calvo sent a low strike wide as Costa Rica threatened again before Nemanja Matic and Luka Milivojevic combined to find Milinkovic-Savic, whose overhead kick was saved by Navas with the flag up in any case.
The Ticos were the surprise of the last World Cup, reaching the quarterfinals in Brazil before being ousted by the Netherlands on penalties.
Serbia's attacking players had a field day against a struggling Los Ticos defence, which was set up as a back three - with the wing-backs often leaving their flanks exposed at times.
However, Navas had to take the ball out the back of his net six minutes later after Kolarov curled a free-kick inside the near post from 22 yards out on the right.
Serbia, who last appeared in the finals in 2010, were eager to show their worth in their first game back on the showpiece event.