Bayern dominated an incident-packed first half and will wonder how they made it to the break only 2-0 ahead. Diaz needed less than four minutes to break the deadlock, firing home after Lucas Chevalier had blocked a shot from Michael Olise following a quick counter.
The German giants kept getting in behind PSG and saw Aleksandar Pavlovic fire narrowly wide and Serge Gnabry hit both posts with one shot before Diaz bagged his brace. This time he caught Marquinhos napping, nicking the ball off the dawdling Brazilian's toes and then slotting another strike home.
Josip Stanisic thought he’d made it 3-0 just before the break but saw his effort ruled out for offside, before Diaz went from hero to villain. The Colombia international lunged in two-footed on Achraf Hakimi in a challenge which saw the PSG star helped off the pitch in tears and the referee brandish the red card for Diaz after a VAR check.
The dismissal saw Vincent Kompany take off the influential Gnabry at half-time for Tom Bischof, with the new man booked almost immediately after arriving. PSG went on to enjoy plenty more possession but struggled to work Manuel Neuer in the Bayern goal initially.
Goncalo Ramos and Joao Neves were sent on as Luis Enrique tried to find a way back into the game and the breakthrough eventually came. Neves halved the deficit on the volley after a great ball in from Kang-in Lee with just 15 minutes of normal time remaining.
The goal gave PSG hope and the chances continued to come. Neves headed another opportunity wide as PSG kept on pushing for an equaliser but Bayern clung on for a huge win against the defending champions.