Chelsea were in a position where they wanted to get a good fee for the 29-year-old, but it was quite clear that Costa wanted to return to Atletico Madrid and they knew he wasn't going to play again for Chelsea, seemingly driving his price down.
Costa agreed a return to Atletico in September but was unable to play until the new year due to the Spanish club's transfer ban.
"I can't ask for more in this second debut for Atletico".
Costa started the move that led to his goal, driving forward before moving the ball wide, allowing Juanfran to whip in a low cross that Costa clipped past Lleida keeper David Oliveros.
The Brazil-born Spain global appeared to hurt his right knee in scoring, and received lengthy treatment on the sidelines, although he played on to see another sub, Antoine Griezmann, finished the scoring with a deflected free kick in added time.
Coach Diego Simeone sent Costa on in the 64th minute.
'It is great for me to play for Atletico Madrid again, the club are very important to me and I am very happy with this. Diego gives us pace, strength, commitment. what we expect from him.