Mourinho's Chelsea F.C. plays at Atletico Madrid's Vicente Calderon Stadium on Tuesday with its domestic title hopes floundering following a 2-1 loss to last-place Sunderland on Saturday. Atletico Madrid, meanwhile, secured an eighth straight victory to move within three wins of its first league title since 1996.
Mourinho made it as far as the semifinals twice during his previous spell with the Blues before guiding Inter Milan to the title in 2010. Since then, he has three straight visits to the semifinals with Real Madrid, losing each time.
Chelsea faces the only unbeaten club left in the competition, with Atletico Madrid having stifled Barcelona and AC Milan on its way to its first European Cup semifinal since 1974.
Here are five things to know before the first match of the two-legged series:
WELCOME BACK JOSE
Atletico Madrid coach Diego Simeone would like to pick up where he left off against Mourinho, following the Portuguese coach's time in Spanish football.
Mourinho won two trophies in three seasons at Real Madrid, but capped his worst season as a football coach with a loss to Atletico Madrid in the Copa del Rey final last year.
That stinging defeat helped send Mourinho bolting back to Chelsea and propelled Atletico Madrid on its improbable run that has it on the verge of becoming the first Spanish club apart from Real Madrid or Barcelona to lift the Spanish title since Valencia did in 2004.
''It's going to be a competitive game between two teams that play a similar style,'' Atletico Madrid captain Gabi Fernandez said. ''Mourinho's teams are always tactically prepared and will look to impose their way.''
Chelsea looks likely to be without one of its top attacking weapons for the first leg, with Eden Hazard still not back in training after a calf injury.
The Belgium winger limped out of the quarterfinal second leg against Paris Saint-Germain on April 8 and has missed Chelsea's last two games.
The most recent update on his condition came on Friday, when assistant manager Steve Holland labelled Hazard a ''major doubt.''
Chelsea will definitely be without right back Branislav Ivanovic, who is suspended for the first leg.
Atletico Madrid's attack received a major boost with the news that playmaking midfielder Arda Turan will be available against Chelsea.
The Turkey international has been sidelined by a groin injury since a 1-1 draw at Barcelona in the opening leg of the quarterfinals. Turan's return will aid Atletico's attack with Spain playmaker Koke having been forced to be the main provider for striker Diego Costa.
Diego Costa scored his 27th league goal in Atletico Madrid's 2-0 win over Elche on Friday to take his season tally to 35 in all competitions.
While much of Atletico's success can be attributed to the boot of striker Diego Costa, its defense has not only been Spain's best but Europe's too.
Atletico Madrid has stifled opponents like Lionel Messi and Mario Balotelli with ease and has conceded a competition-low five goals.
While center backs Miranda and Diego Godin have been superb this season, goalkeeper Thibaut Courtois has been outstanding without a dip in form. Atletico will be counting on the 21-year-old Belgium international against his mother club after UEFA ruled that Courtois could not be left out of the series due to any pre-agreed contractual agreements with Chelsea over his loan deal.
Chelsea striker Fernando Torres will make his return to his boyhood club this week amid increasing speculation he could be back at the Vicente Calderon for good before next season.
Torres spent the first six years of his professional career at Atletico Madrid, captaining the team for a spell before leaving Spain for Liverpool in 2007.
His career has stalled at Chelsea since his 50-million pound (then $81 million) move there in 2011, and the prospects of an emotional return to Atletico were raised after comments by coach Diego Simeone last week.
It would be a major surprise if Torres started the second leg, with the striker appearing to have slipped to third in the pecking order behind Samuel Eto'o and Demba Ba.