Left-back Gallas hit the goal of his life with his right foot from 20 yards as the game ticked into injury time, the ball arrowing beyond Paul Robinson and into the corner to secure a 2-1 win for the home side.
Michael Essien had earlier opened the scoring as Chelsea had the better of the first half but Jermaine Jenas gave us a real boost by levelling just before the break.
The midfielder then had the best chance of the second half as he sprinted onto Ledley King's pass only for Petr Cech to save the one-on-one.
Robinson then produced a magnificent save to tip Didier Drogba's drive onto the post and it looked like a point each until Gallas struck in added time.
"I feel for the lads and they are all bitterly disappointed in the dressing room," said Chris afterwards.
"We're well aware that this is a difficult place to come but we are upbeat about the performance.
"We started very bright, did well on the counter-attack and, in the second half, we looked more solid and coped with them fairly well.
"We were up against real quality. We came away to the best team in the country but most people would say that we deserved something from the game."
Chris Hughton said the lads were devastated after William Gallas clinched late victory for Chelsea at Stamford Bridge.