Record winners Real Madrid and title holders Manchester City played to a thrilling 3-3 draw while Harry Kane continued to haunt Arsenal in their 2-2 with Bayern Munich in the Champions League quarter-finals on Tuesday.
City led early from Bernardo Silva's clever free-kick and went back on top at 3-2 from Josko Gvardiol in the 71st, five minutes after a stunner from Phil Foden at the Bernabeu.
But Real fought back twice in the 200th Champions League match of their coach Carlo Ancelotti.
They went 2-1 up within 12 minutes after Silva's opener when Ruben Dias deflected Eduardo Camavinga's shot into his own net and Rodrygo scored on the counter for 2-1, and Federico Valverdo was on target for the final score in the 79th.
In London, Bukayo Saka fired Arsenal ahead in the 12th, their former player Serge Gnabry levelled in the 18th, and ex-Tottenham great Kane netted for the sixth time at Emirates Stadium with a 32nd-minute penalty to put Bayern 2-1 up.
However, Leandro Trossard salvaged a draw for the hosts with 14 minutes left.
There is now all to play for in the return legs next week in Manchester and Munich, with the winners meeting in the semi-finals.
The matches took place amid beefed up security after an Islamic State terror threat via a media outlet linked to the group.
That will also concern the other first leg matches on Wednesday: Paris Saint-Germain v Barcelona and Atletico Madrid v Borussia Dortmund.