Chelsea late show deepens Crystal Palace crisis
Palace have won just three times in 19 games and were undone late on after Gallagher equalised within two minutes of the second half.
Conor Gallagher struck twice to condemn his former club Crystal Palace to a damaging 3-1 defeat on Monday and keep Chelsea in the hunt for European football next season.
The injury-ravaged Eagles were on course for a huge win in their battle to remain in the Premier League when Jefferson Lerma's long-range strike opened the scoring.
But Palace have won just three times in 19 games and were undone late on after Gallagher equalised within two minutes of the second half.
Gallagher fired home his second of the night and Enzo Fernandez added the third in stoppage time to lift Chelsea up to 10th and within two points of seventh.
The defeat leaves Palace still just five points above the relegation zone in 15th.
"It was extremely cruel but the game is about goals and unfortunately we made mistakes which led to goals," said underfire Palace boss Roy Hodgson.
The home side were decimated by key injuries with all three of their star players Eberechi Eze, Michael Olise and Marc Guehi ruled out.
Hodgson and the club's board are under attack from the fans and banners held up before kick-off took aim at a "weak club culture" and "weak transfer policy."
But Palace more than held their own for the first 45 minutes thanks to another lacklustre Chelsea performance away from home.
"We started really flat, we didn't show enough intensity. It was a really tough first 45 minutes," said Chelsea boss Mauricio Pochettino.
"Second half we started really well, scored the 1-1 and it allowed us to manage the game."
Pochettino had hailed his side's 3-1 FA Cup win at Aston Villa last week as his side's "best performance of the season."
However, it was back to the drawing board for the Argentine in the first half at Selhurst Park as Chelsea were pedestrian in possession and were punished.
Noni Madueke was easily bullied out of possession on the edge of his own box and the ball fell to Lerma to take aim and fire into the top corner beyond Djordje Petrovic.