Diego Costa scored for Atletico Madrid just five minutes into his return as the club cruised to a 4-0 win at Lleida Esportiu in the Spanish Copa Del Rey on Wednesday.
Costa, who rejoined from Chelsea in September but could not play until the transfer window opened this month, came on as a 64th-minute substitute and swept home Atletico's third goal in the 69th minute in the first leg of a last 16 tie.
"I'm really happy to feel like a footballer again and play once more with Atletico Madrid. It was very important for me," Costa said after the match.
"I couldn't have hoped for a better start to my second spell with Atletico. I was given the opportunity to play again and I had the chance to score a goal. That makes me even happier."
Spain international 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.
Costa appeared to have injured himself stretching to score the goal, but carried on and finished the game.
"Costa's return has filled us with enthusiasm," said Atletico coach Diego Simeone. "He brings speed, strength and physicality, which is what we expected of him."
Two goals in four first-half minutes from Diego Godin and Fernando Torres set Atletico up for the comfortable win away to third tier Lleida, with Godin heading home a drilled free-kick after 33 minutes and Torres doubling the lead soon after, just about staying onside to tap home Kevin Gameiro's low cross.
Costa's fellow substitute Antoine Griezmann completed the rout in the final seconds, his deflected free-kick sailing past Oliveros giving Simeone's side a seemingly unassailable lead ahead of Tuesday's second leg at the Wanda Metropolitano in Madrid.
Meanwhile, Vincenzo Montella got off to a winning start as Sevilla coach, the former AC Milan coach's new side beating Cadiz 2-0 thanks to goals from Nolito and Jesus Navas.
Barcelona and Real Madrid play their respective first leg clashes with Celta Vigo and second-tier Numancia on Wednesday, with Barca coach Ernesto Valverde set to rest Lionel Messi and Luis Suarez, who both returned late from holidays in South America, as well as captain Andres Iniesta.