Real Madrid were far from their best but scraped a 2-0 win over Granada to move level on points with Atletico Madrid at the top of La Liga.
Two minutes of inspired attacking by substitute Asensio culminated in his pass for Casemiro to head in the 57th-minute opener at Madrid's Alfredo Di Stefano Stadium.
Karim Benzema scored Madrid's second goal in the game's final seconds with Granada caught out as they searched for an equaliser.
Madrid's fifth league victory in a row has them in second place behind city rivals Atletico on goal difference.
The title chase is shaping up to be a contest between the two capital city rivals.
They are both six points ahead of Real Sociedad and Villarreal.
Fifth-place Barcelona are eight points back.
Atletico have games in hand over the rivals having played just 13 times with Barcelona 14, Madrid and Villarreal 15, and Sociedad 16.
Asensio replaced forward Rodrygo Goes in the 38th when the 19-year-old Brazilian grabbed his right thigh and asked to be replaced.
Earlier on Wednesday, Celta Vigo earned a 1-1 draw at Getafe in a mid-table battle.