The Blues had started the final day of the Premier League season in third spot, knowing victory over their mid-table opponents would guarantee a place in the group stages of Europe’s prestigious knockout club competition.
Tuchel’s side carved out the better chances but fell behind when Bertrand Traore’s attempt went in off the underside of the crossbar following Matt Targett’s corner.
It went from bad to worse for Chelsea when Edouard Mendy was injured, making him a doubt for next Saturday’s Champions League final with Manchester City.
Substitute keeper Kepa Arrizabalaga was beaten by Anwar El Ghazi’s second-half penalty after former Chelsea player Traore was fouled by Jorginho, before Ben Chilwell pulled one back for the visitors from close range.
Chelsea finished the game with 10 men after captain Cesar Azpilicueta’s straight red card for a foul on Jack Grealish, but Leicester’s home defeat by Tottenham means Tuchel’s side finish the season in fourth on 67 points – one more than fifth-placed Leicester.
From ninth to Champions League spot
On a dramatic final day, Tuchel and his players experienced a full range of emotions before it was finally confirmed they had secured a Champions League group place.
It is an impressive achievement considering the Blues were ninth when Tuchel took charge in January, and of course his side could yet end the season by being crowned champions of Europe.
But they will have to play better – and show more discipline – than they did against Villa if they are to win in Porto next weekend after losing for only the third time in the league under the German.
Traore was unmarked when he fired Villa ahead, while Jorginho’s foul on the Villa midfielder gifted the hosts a second goal from the spot.
Azpilicueta can have few complaints about his red card but most worrying for Tuchel will be the fitness of Mendy.
The Senegal keeper has settled well since arriving from Rennes in September and proved a calming influence on the defenders in front of him. Tuchel will hope his injury does not hamper his plans for next weekend.
While Aston Villa’s players head off for a break, Chelsea now turn their thoughts to Saturday’s Champions League final against Manchester City in Porto