Dennis Wise's fourth red card of the season overshadowed a stunning debut by Mikael Forssell in which the teenager scored two spectacular goals.
Forssell struck twice in the first six minutes of the second half to kill off Oxford and set up a 4-2 FA Cup replay victory which earns Chelsea an away trip to Sheffield Wednesday in the fifth round.
But the Finnish striker will lose the headlines to Wise who now faces a four-match ban and hefty FA fine, which will take the number of games he has missed this season through suspension to 14.
Wise was booked two minutes before half-time for a handball and then a complaint to the linesman. But he got his marching orders after 75 minutes when he blocked Dean Windass's shot with his hand and conceded a penalty from which Windass made the score 4-2.
Wise must surely owe an apology to the promising 17-year-old striker who made his full debut at Stamford Bridge in this match.
He brought the game to life just 46 seconds into the second half when he cut in from the left and curled the ball into the top far corner.
He followed that up after 52 minutes with a fierce dipping drive from 20 yards which finally killed off the First Division team. Oxford had stunned Chelsea with a goal inside the first five minutes. It was almost a carbon copy of the goal which had given them the lead at the Manor Ground a fortnight ago as this time a right wing corner from Jamie Cook was headed in by Phil Gilchrist courtesy of a deflection off Marcel Desailly.
Gianfranco Zola, making his 100th appearance for Chelsea stood out for the home side and set up an equaliser after 12 minutes. He found Wise with a low cross from the left and the midfielder slotted home to become, incredibly, the first English player to get on the score-sheet for Chelsea this season.
Wise returned the compliment after 39 minutes when he released Zola on the right edge of the box and the Italian chipped the ball beyond the advancing goalkeeper and in off the far post.
Player-manager Gianluca Vialli dropped himself to give the man half his age the chance and he was certainly left with something to think about in the future. But Vialli must first think a little more about the problems caused to him by his loyal but headstrong skipper.
Chelsea: De Goey, Petrescu, Desailly, Leboeuf (Terry 59), Le Saux, Wise, Morris, Di Matteo (Goldbaek 74), Babayaro, Zola, Forssell (Nicholls 66). Subs Not Used: Hitchcock, Newton. Sent Off: Wise (75). Booked: Babayaro, Wise. Goals: Wise 13, Zola 40, Forssell 46, 53.
Oxford Utd: Jackson, Robinson, Watson, Gilchrist, Powell, Banger (Remy 64), Gray, Tait, Cook (Beauchamp 51), Windass, Murphy (Francis 59). Subs Not Used: Wilsterman, Weatherstone. Booked: Jackson, Tait. Goals: Gilchrist 5, Windass 77 pen.
Referee: M Reed (Birmingham).
