Boos rained down on the Chicago Fire players as they left the Toyota Park field at halftime Sunday.

There were only cheers for the Fire after the game.

Nemanja Nikolic scored twice in the final 26 minutes to give the Fire an all-important 3-2 victory against the struggling Philadelphia Union.

Together with his first-half goal, Nikolic's hat trick gives him 24 goals for the season. He leads the league Golden Boot race by 3 with a game to play.

More importantly, the Fire gained in its battle for playoff positioning. It moved past Atlanta United into third place and is just 1 point behind New York City FC for the first-round playoff bye that comes with a second-place finish.

"Well, we want second place, so we're going to go to Houston (next week) to win the game and we're going to go to Houston to get second place and take care of what we can control," Fire goalkeeper Matt Lampson said.

Despite the comeback victory against the going-nowhere Union, coach Veljko Paunovic wasn't in a mood to celebrate. The Fire did not play well in the first half, quickly giving up the lead after Nikolic's first goal, which came in the third minute.

"I think the whole second half, that's the performance we needed," Paunovic said. "We are proud of the character that we showed. The reaction was good in the second half.

"Obviously, two different parts of the game. First half after the third minute we actually thought that the game for us was over, and that's unacceptable. We cannot ever again have that performance or that mindset."

"The energy level dropped as soon as they scored, right after," Lampson added. "A couple of mistakes defensively. It just wasn't good enough tactically, technically in the first half from everybody."

Halftime was the turning point, particularly the substitution of speedy midfielder David Accam, who rested an injured hip in the first half. Accam earned the penalty kick that became Nikolic's second goal and had a secondary assist on the third.

Left back Brandon Vincent added 2 assists, but the day belonged to Nikolic.

"I feel really good, and not just about hat trick, about the victory, because it was really important for us," said Nikolic, who had fans chanting his nickname, "Niko", after the game. "First half was not too great, but I think we show attitude. We show personality."

Nikolic also could tie the league record for goals in a season with another hat trick in the regular-season finale.

The Fire again played without German midfielder Bastian Schweinsteiger due to a leg injury. Schweinsteiger said after the game he felt "so-so" and said "maybe" when asked if he would play at Houston.