The 24-year-old was decisive in the victory at Selhurst Park, netting twice in the second-half as Mauricio Pochettino's men came from a goal down to secure a crucial three points.
Gallagher produced two smart finishes to cancel out Jefferson Lerma's opener before Enzo Fernandez made sure of victory deep into added-time.
The win saw Chelsea bounce back from consecutive league defeats to Wolves and Liverpool and climb into the top-half of the table.
Gallagher was instrumental in Chelsea's turnaround and his performance was compounded by an incredible running stat that left the star shocked.
The England international, who scooped the Player of the Match award, admitted his calves were 'cramping up' in the second-half when interviewed on Sky Sports' Monday Night Football panel.
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He was told the cramp is likely to be a result of the distance he covered during the game, which equated to a whopping 13km.
A stunned Gallagher responded: "Wow that's far innit," before sharing a laugh with the studio guests.
He continued: "I always want to run as hard as I can for the team but it didn't feel like I ran that far, to be fair, because we had so much of the ball. But that's good, I'm happy."
Gallagher has featured in all but one of the Blues' league fixtures this season and appears to be a key component in Pochettino plans.
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But his future continues to be a source of speculation with moves to Newcastle and Tottenham mooted both last summer and during the recent January transfer window.
Chelsea are believed to value their academy star at around £50million as they contend with Financial Fair Play regulations.
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But it has been business as usual for the Three Lions star who appears keen to stay and prove his worth at Stamford Bridge.
Gallagher is doing his hopes of inclusion in England's Euro 2024 squad no harm, either.
The midfielder was an unused substitute at the 2022 World Cup in Qatar and will hope to play a more prominent part in Germany this summer, if selected.