The Nigerian headed in his fourth Blues goal from Willian's whipped free-kick on 66 minutes and Oscar made sure of the win with a swerving strike five minutes laterChelsea booked their place in the fourth round of the FA Cup with a hard-fought 2-0 victory at in-form Championship side Derby County.
John Obi Mikel marked his 300th appearance for Chelsea with his fourth goal for the club to break the deadlock, rising to meet a Willian free-kick in the 66th minute at the iPro Stadium.
Oscar then doubled Chelsea's lead four minutes later with a powerful strike from the edge of the penalty area that Derby goalkeeper Lee Grant was unable to keep out.
Ramires, who was booked for diving in the second half, also clipped the top of the crossbar late on as the seven-time FA Cup winners finished the third-round encounter strongly.
|VIEW FROM THE IPRO STADIUM
|By Sam Lee
So it was fairly easy for Chelsea in the end. The hosts, backed by a noisy crowd, came out of the traps strongly but faded off as the Blues wrested control of the match.
Jose Mourinho will be pleased to go through with little fuss, of course, but his side did not exactly click and on another day could have easily drawn a blank - but when Mikel scores a header you know it's going to be your day.
Will Hughes, Derby's talented youngster, had an afternoon to forget as the Rams toiled for large parts of the game, especially after the break.
There was no game time for Juan Mata, who has hardly been overworked in recent weeks, but aside from that the Chelsea fans will go home happy.
Victory for Jose Mourinho's side means Chelsea will face Stoke City at Stamford Bridge in the next round in the only all-Premier League tie.
The hosts were forced into two changes as injuries ruled out Craig Bryson (groin) and Johnny Russell (fractured cheekbone), so Jeff Hendrick and Simon Dawkins came in.
Mourinho made six changes from the Chelsea side that beat Southampton on Wednesday as Schwarzer took over in goal from Petr Cech and Samuel Eto'o replaced Fernando Torres in attack.
Derby created the best chance of the opening exchanges with 13 minutes gone as they attacked down the left, but Jamie Ward was unable to meet Craig Forsyth's cross and Ashley Cole cleared the danger.
A mistake by Michael Keane in the 22nd minute saw the unmarked Eto'o released into the Derby half. Andre Wisdom and Jake Buxton muscled the Cameroon international off the ball, however, before he could get his shot away.
Chelsea finished the half the stronger, but wasted chances to break the deadlock through Ramires and Oscar.
Clear-cut opportunities after the restart were few and far between before Chelsea took the lead just after the hour.
Mikel rose unmarked at the front post to meet a Willian free-kick from the left and his flicked header beat Grant from five yards.
Oscar finally got his goal in the 70th minute with a well-struck effort from inside the penalty area. The Brazilian created room on the edge of the box and lashed a shot at goal that found a way past Grant.
Substitute Torres, who had replaced Eto'o, had two chances in the closing minutes of the match, but was denied by Grant on both occasions and the woodwork frustrated Ramires as Chelsea went in search of a third.