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The Blues and Porto return to the neutral venue of Seville, with Chelsea leading 2-0 from last week's first leg - holding the advantage of two away goals.
Goals from Mason Mount and Ben Chilwell propelled the Blues to a comfortable win in the first meeting and, once again, the Portuguese champions have been left with a mountain to climb to salvage their European season.
Tuchel's side - currently fifth in the Premier League - also face Manchester City in the FA Cup semi-finals on Saturday.
Having only lost once in 17 games under Tuchel, Porto will almost certainly have a fight on their hands in the second leg.
The winner will face either Real Madrid or Liverpool in the semi-finals.
The FA Cup and Premier League may be playing on Chelsea's minds slightly, given that they have more or less completed the job in this tie.
Chelsea are unbeaten in the Champions League so far this season and could become the first English club to go unbeaten across their first ten games in a season in the competition since Liverpool in the 2017-2018 season.
Close but no cigar has been the theme of Porto's Champions League endeavours in recent years, having never managed to advance past the quarter-final stage of the tournament since their triumphant venture in the 2003-2004 campaign under Jose Mourinho.
While their historic last-16 victory over Cristiano Ronaldo's Juventus cannot be overlooked, Sergio Conceicao's side must score at least twice against Tuchel's resilient Blues to stand a chance of turning the tie around.
Despite Porto's domestic good form, overturning a 2-0 deficit is surely too much of a climb for the 'visitors'.
With that being said, Chelsea are more than likely to march into the semi-finals here.
Thomas Tuchel is blessed with a fully-fit squad for Chelsea's Champions League quarter-final second leg in Seville.
Thiago Silva could earn an immediate recall to defence after serving a domestic suspension against Crystal Palace.
Meanwhile, a late decision will be made on N'Golo Kante's involvement for Chelsea in tonight's game.
The midfielder has made back-to-back substitute appearances since recovering from hamstring tear - but Thomas Tuchel does not want to take any risks ahead of Saturday's FA Cup semi-final against Manchester City and a hectic run-in to the end of the season.
Chelsea are 17/20 to win tonight, with FC Porto priced at 31/10 to come away with victory. A draw is priced at 27/10.
Odds are correct at the time of publication and are subject to change.
Chelsea are firmly in the driving seat to reach the semi-finals of the Champions League this evening.
BT Sport will be televising tonight's match live on BT Sport 2, with coverage beginning at 7pm (GMT).
Meanwhile, BT Sport subscribers will be able to watch the match online via website of the BT Sport app.
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