Four days after seeing their hopes of a sixth successive scudetto crushed in a 3-0 defeat by rivals AC Milan, Inter's hopes of retaining the Champions League were also in tatters after another night of defensive calamity at the San Siro.
Andrea Ranocchia's own goal and Cristian Chivu's second red card in as many games either side of the hour summed up Inter's defensive misfortunes on a dismal night in Milan.
It was the first time a team defending the European Cup have conceded five goals in a match home or away and added to the pressure on coach Leonardo, the second man to occupy the hotspot since Mourinho after Rafa Benitez's sacking in December.
The humiliation came against a Schalke 04 team who have themselves had a turbulent season and were playing only their second game under new coach Ralf Rangnick who was forced to reshuffle the side after injuries to four key players.
Bundesliga runners-up last season, Schalke are a modest 10th in the Bundesliga and last month fired coach Felix Magath under pressure from fans angry at his increasingly all-powerful role within the club and controversial transfers.
Yet it could have been completely different.
Dejan Stankovic scored an extraordinary goal after less than a minute and Diego Milito, last season's Champions League hero, notched his first in this season's competition as Inter twice led in the opening half.
Leonardo put a brave face on a situation in which his team are five points behind Milan in Serie A and needing a big win in Gelsenkirchen next week to say in the Champions League.
"Of course, a lot has changed in these four days," he told reporters. "But we have to change this situation... We must stay together and we must try to forget these two heavy defeats.
"The first thing is to give our heads a rest. It's a very mature squad, we need to use our energy on the pitch."
HEADED CLEARANCE
Inter could not have made a better start. With only 54 seconds played, Schalke goalkeeper Manuel Neuer rushed out of his area to head away Esteban Cambiasso's long ball forward only to see his clearance land at the feet of Stankovic.
The Serb, who went off injured in the 24th minute, produced an exquisite volley from just inside the halfway line which flew over the bemused goalkeeper into the net.
But two headed chances for Raul showed that Inter's defensive frailties were there to be exposed and it was no surprise when Joel Matip levelled after 17 minutes.
In an end-to-end game, Milito, who scored both goals in last season's 2-0 final win over Bayern Munich, broke his duck this season, side-footing Inter back in front in the 34th minute from fellow Argentine Cambiasso's header.
But Brazilian Edu, little known in his own country, sent Schalke's famously diehard fans into raptures by equalising five minutes before the break, scoring at the second attempt after his better-known compatriot Julio Cesar saved his first effort.
The defining moments
