The holders appeared likely to exit the FA Cup after going 2-0 down 11 minutes into the quarter-final at Old Trafford and many wondered if Rafael Benitez's spell in interim charge would come to a premature end as a result of a heavy defeat to an old rival.
But Chelsea responded with second-half goals from substitute Eden Hazard and Ramires to force a replay, while Mikel too was influential after coming off the bench.
"Let's hope this game will put us back on a good track and we keep going on from here to end the season very well," Mikel said.
"This result has come at a crucial time where we just have to start putting on good performances but the tie is not yet done.
"You can never write off Manchester United at any time. At Stamford Bridge we have to make sure we put this tie away."