"We got a little desperate there at the end," Contreras said. "Our guys started shouting at each other, saying things."
He added the Eagles tried to force the ball too much.
"We got away from trying to do the easy things," he said.
The Eagles also were playing a few men down. Contreras suspended three starters because they played in an outside league.
Southwest led 1-0 after a late first-half goal by Juan Garcia. But Desert Hot Springs stormed back early in the second half, scoring three goals in the span of six minutes, before dropping back and playing a defensive game the final 25 minutes of the contest.
Southwest's starting goalie, Ivan Ochoa, shut out the Golden Eagles, but he was removed six minutes into the second half, and Desert Hot Springs capitalized, scoring its first goal two minutes later.
While Ochoa was not scored upon, he still was pulled as part of Contreras' game plan. Because it was not a league game, the Eagles' coach wanted to give some of his reserves some playing time.
"I told our guys we would be making changes in the second half," Contreras said.
"All we need to do is win at least half of our league games," he explained.
If the Eagles do that, they will qualify for postseason play.
Contreras said because Southwest won the Grossmont Tournament in San Diego last month, the Eagles are ranked in the top 10 in the CIF's San Diego Section and virtually assured of a playoff berth provided they finish at least in the middle of the pack in league.
Garcia scored Southwest's lone goal with less than five minutes remaining before halftime. Joshua Mora centered an indirect kick from the right side and Garcia dove for the ball, just heading into the net inside the left upright.
Eight minutes into the second half Desert Hot Springs scored off a shot by Ivan Rivera. Two minutes later Miguel Jimenez connected with a quick strike, taking a pass from midfield and slicing it past the Eagles' goalie.
Southwest looked to tie the game seconds later. Mora passed the ball ahead to Luis Montes, who centered it for Jorge Renteria. But Renteria's shot on goal sailed just over the crossbar.
Rivera put the game out of reach moments later with his second goal of the game for Desert Hot Springs. He had a wide open net as the Eagles' keeper was out of the cage making a stop on a rushing attacker.
A few minutes later Southwest nearly picked up its second goal when Mora passed ahead to Renteria. Renteria split two defenders before taking a shot that sailed wide.
Southwest had a few other shots on goal down the stretch but none found the mark.
The Eagles (6-4-3) will play at Holtville at 6:30 tonight.