Chelsea dominated possession for much of the contest but had fallen behind in the opening period when Jefferson Lerma rifled an unstoppable shot from 25 yards beyond Djordje Petrovic.

The Blues needed to react in the second half and did so immediately as Gallagher’s fine cushioned volley from a Malo Gusto cross brought us level and swung momentum in the contest our way.

It appeared as though we'd be frustrated in our attempts to find a winner but, as the clock ticked into the 90th minute, Cole Palmer teed up Gallagher and he swept the ball home from the edge of the box.

Enzo Fernandez then completed a fine breakaway with an excellent finish to wrap up a hard-fought win for Mauricio Pochettino's side.

A slow start

Only one change was made to the Chelsea side that started the FA Cup victory at Aston Villa: Thiago Silva replaced the injured Benoit Badiashile in defence.

The Blues showed the same composure on the ball that had served them so well at Villa Park, with possession dominated in the early stages.

Yet it was Petrovic who had to make the first save of note as the Serbia international reacted quickly to deny a low effort from Jean-Philippe Mateta after a loose pass from the otherwise impressive Malo Gusto.

At the other end, Chelsea searched for a way through the Palace backline and Ben Chilwell drove dangerously into the box only to lose his footing at the crucial moment and the chance fizzled out.

A Palace stunner

With very little between the sides in terms of goal threat, Palace made the crucial breakthrough on the half-hour mark.

Noni Madueke’s pass on the edge of the Chelsea box was intercepted and Lerma collected the ball and unleashed a ferocious drive to leave the Blues stunned. The movement on the shot, unfortunately, gave Petrovic no chance.

Chelsea continued to control the ball for the remainder of the first half and created a big chance just before the break as Gallagher broke into the box and released a shot that rolled wide. It meant we were behind at half-time.

Back on terms

Pochettino introduced Christopher Nkunku at half-time and received an instant response from his players to a sluggish 45 minutes.

Just as the travelling Chelsea supporters’ version of the Bob Marley classic Three Little Birds echoed around the stands, the crucial equaliser arrived. Perhaps every little thing was going to be alright for the Blues.

It was an excellent pass from Moises Caicedo that enabled Gusto to break behind the Palace backline, and his weighted pullback was smashed home by Gallagher, who struck once again against his former loan club.

The goal set the tone for a period of play that saw Pochettino’s side pin the hosts in their half – and Palmer very nearly got his name on the scoresheet with an effort that flashed narrowly wide of the post.

Carrying a threat

Palace's biggest threat came on the counter and the Blues were given a scare when Mateta found space in the box after Matheus França cut through our defence with an excellent pass.

Thiago Silva made an important block to deny the Palace forward but in doing so suffered an injury and was immediately replaced by the returning Levi Colwill.

We continued to press forward and adventurous play from Caicedo was nearly rewarded when Chilwell flashed an effort narrowly over the crossbar. Nicolas Jackson then guided a header wide after a clever cross from Gallagher, who had started to take control in midfield.

Petrovic still had work to do and the Chelsea goalkeeper did it well to deal with Franca’s powerful shot after another quick Palace break.

Late drama

The chances continued to come for Chelsea and what appeared to be a pivotal one fell the way of substitute Raheem Sterling. The England international was found by Palmer but his effort from inside the box was blocked. Axel Disasi was then denied by Henderson.

It appeared as if Palace would hold out, but they hadn’t banked on Gallagher, who popped up in injury time to drive home a low effort, beat Henderson, and cause wild celebration in the away end.

And when moments after the restart Chelsea launched a counter through Palmer, the victory was secured. It was Enzo who finished the move – his second goal in a week – and the points were on the way back to west London.

What it means

The victory moves us back into the top half of the Premier League table. The Blues now sit tenth and two points off a European place.

What is next

We return to Premier League action on Saturday with a trip to Manchester City at the Etihad Stadium, kick-off is 5.30pm.

The teams

Chelsea (4-3-3): Petrovic; Gusto (Gilchrist 83), Disasi, Thiago Silva (Colwill 60), Chilwell (C); Gallagher, Caicedo, Enzo; Madueke (Nkunku 45), Palmer, Jackson (Sterling 78)
Unused subs: Bergstrom, Mudryk, Chalobah, Chukwuemeka, Casadei.
Scorer: Gallagher 47, 90, Fernandez 93

Crystal Palace (4-2-3-1): Henderson, Munoz, Andersen (C), Richards, Mitchell; Lerma, Wharton; Ayew, Hughes (Ahamada 78), Franca (Edouard 83); Mateta.
Unused subs: Johnstone, Ward, Tomkins, Schlupp, Clyne, Riedewald, Ozoh.
Scorer: Lerma 30

Referee: Michael Oliver