Atletico Madrid coach Diego Simeone said Diego Costa's arrival at the club has led to better play from Antoine Griezmann and has also served as a catalyst for the team's turnaround.
Costa returned to Atletico from Chelsea in September, but he was only eligible for selection in January, once Atletico were able to register new players following a transfer ban.
Atletico, second in La Liga, have taken 25 of a possible 27 points since the turn of the year to put pressure on leaders Barcelona.
Griezmann has rediscovered his goalscoring touch while playing with Costa as he has scored 13 of his 16 goals in all competitions in 2018, including a career-best four in Wednesday's 4-0 triumph over Leganes.
"Our season until December was good," Simeone said, according to Marca. "Costa not only improves Griezmann but the whole team for what he transmits and that is what is happening to us right now. We are going through a good run and from being humble, we will continue as we've always done."
Griezmann, whose heroics on Wednesday allowed him to surpass the 100-goal mark with Atletico since joining the club from Real Sociedad in summer 2014, also said Costa's presence has made him a better player.
"Having him there gives me a lot of freedom, and I can do what I like the most, which is to receive on the wings and get inside," Griezmann told Onda Cero radio. "It also gives me a reference in attack. Costa is the one that clashes with defenders and I'm there waiting for the rebound."
Simeone said he is not surprised by Griezmann's improved form.
"He's had runs like this one in previous seasons," Simeone said. "He is extraordinary and the team accompanies him so that he is able to deliver like this. The passes he got [against Leganes] were fantastic and with his talent, he was able to finish them off."
Atletico are riding an eight-match winning streak in all competitions heading into Sunday's game at Barcelona. They are four points adrift of the La Liga leaders, who visit Las Palmas on Thursday.
"We have to prepare as well as we can for this game as we face a rival that has won everything and has yet to lose," Simeone said.