After an outstanding second-half comeback by Rafa Benitez's men in the first game at Old Trafford to stay in the hat, this victory booked The Blues a place in the semi-finals at Wembley, where Ba would score again in a 2-1 defeat at the hands of Manchester City.
Meanwhile, Sir Alex Ferguson's side would go on to win their 13th Barclays Premier League title with the Scotsman bringing an end to his illustrious managerial career at the end of the season.
Ba breaks the deadlock
The Senegalese international scored the winner four minutes into the second-half in a moment of real quality. Juan Mata, who would leave for United just nine months later, provided the pass, with Ba pulling away from Rio Ferdinand to hook a fine finish beyond a despairing David De Gea.
Clean sheet was no mean feat
United were without Wayne Rooney, who picked up a groin injury playing for England against Montenegro in a World-Cup qualifier during the International break. The Red Devils still started the match with a front-two of Danny Welbeck and Javier Hernandez and were able to bring the Golden-Boot winner, Robin Van Persie, on from the bench. However, all that attacking firepower still couldn't breach Petr Cech's goal on the day, and the visitors failed to score for the first time in 23 matches in all competitions.
Where are they now?
After leaving the club to join Arsenal in 2015 where he retired at the end of last season, Cech has since returned to Stamford Bridge to take up the role of Technical and Performance adviser.
The Spaniard is the only player in the current squad who started this match. He has made 37 appearances in all competitions so far this season.
At the age of 36, the Serbian is still playing and is captain at his current club, Zenit Saint Petersburg.
Like Cech, Luiz has made the switch from South-West to North London to join The Gunners, leaving the Bridge last summer.
The Brazilian has made 32 appearances in all competitions this season.
He officially announced his retirement in August last year, and has since become a Youth Coach at Chelsea as well as an occasional TV pundit for Sky Sports.
The Nigerian made the headlines a few weeks ago after terminating his contract at Trabzonspor by mutual consent over Coronavirus fears.
Mikel said he 'did not feel comfortable' playing football during the ouotbreak after the Super Lig continued to play matches behind closed doors.
He had only joined the club last year, and had a deal until May 2021 with the Turkish side.
Ramires left the Blues to join Chinese Super League side, Jiangsu Suning, in 2016. The Brazilian has sinced returned to his home country in 2019, joining Palmeiras.
Hazard left Stamford Bridge last summer, joining Real Madrid for an initially reported fee of 100 million Euros.
The Belgian's debut season in Spain has been riddled with injury. As a result, he has only made 10 appearances for Los Blancos, scoring just once.
Mata won Chelsea Player of the Year in consecutive seasons between 2011-12 and 2012-13. He also scooped up the Players' Player of the Year award that year as he scored 20 goals and provided 35 assists in 68 matches.
Like Ramires, Oscar too left for China, as he joined Shanghai SIPG, where he still plays today
The 34-year-old is currently playing in Turkey for Istanbul Basaksehir, who sit second in Super Lig behind Mikel's former side Trabzonspor on goal difference.