Hugo Mallo put Celta Vigo on the board with a header in the 61st minute and Iago Aspas sealed the victory after a mistake by Athletic Bilbao goalkeeper Unai Simon in the 78th.
Mendy joined Chelsea from French club Rennes on a five-year contract this week, strengthening Lampard's goalkeeping options following Kepa Arrizabalaga's dismal form.
Eibar needed goalkeeper Marko Dmitrovic to step up to salvage a 0-0 draw with Celta Vigo at home in their first LaLiga match of the season.
The come-from-behind victory in Bilbao left Sevilla tied on points with third-place Atlético Madrid and increased its gap to fifth-place Villarreal to six points with three rounds to go. Only the top four qualify for next season's Champions League.
Real Madrid are the only team with a perfect record since the restart. They have had seven straight win since the league resumed, leaving them four points ahead of second-place Barcelona with four matches left.
LaLiga: Real Madrid pick up seventh straight win to move closer to league title, Barcelona beat Villarreal
Sergio Ramos converted a 73rd minute penalty kick to score his fifth goal post-resumption as Real Madrid bolstered their title chances with a seventh-straight victory.
LaLiga: I’m tired of people saying we are winning because of referees, says Real Madrid boss Zinedine Zidane
Zinedine Zidane made his displeasure known following Real Madrid's 1-0 win over Athletic Bilbao, adding that Madrid — current at the top of the table— deserved more respect for their on-field performances.
LaLiga: Villarreal move closer to Champions League spot after win against Real Betis; Valencia suffer third straight loss
Villarreal's Gerard Moreno converted a seventh-minute penalty kick and added to the lead from inside the area in the 30th to become the league's top-scoring Spaniard with 15 goals
LaLiga: Barcelona midfielder Frenkie de Jong set to miss Athletic Bilbao clash after injuring calf muscle
Barcelona midfielder Frenkie de Jong is set to miss the team’s next match against Athletic Bilbao after the club said in a statement on Sunday he had injured the calf muscle in his right leg.
LaLiga: Real Betis fire manager Rubi after three-game winless streak; former player Alexis Trujillo appointed interim replacement
Real Betis has fired coach Rubi after the team’s third consecutive setback since the Spanish league resumed.
LaLiga: Diego Simeone’s Atletico Madrid earn hard-fought victory over Valladolid; Getafe held by Eibar
Atlético Madrid honoured the club’s victims of the coronavirus pandemic and earned a hard-fought victory Saturday in their first home game since the Spanish league resumed.
LaLiga: Marcelo takes knee as Real Madrid make winning return to league; Atletico held to draw at Athletic Bilbao
Real Madrid resumed their Spanish league campaign with a 3-1 win over Eibar on Sunday to keep pace with leader Barcelona.
LaLiga club logos explained: What does the tree on Athletic Bilbao's escudo mean? Is there an English reference to Barcelona's logo?
Aduriz, who also played for Spanish clubs Valladolid, Mallorca and Valencia, leaves Athletic as the club's sixth-highest scorer with 172 goals.
Copa del Rey: Spanish Football Federation heeds to Athletic Bilbao, Real Sociedad's request of playing final in front of fans
The RFEF said it agreed “wholeheartedly” with the two football clubs wishes for fans to attend the match.
The first final between Athletic Bilbao and Real Sociedad, two prestigious Basque clubs, was due to be held on 18 April in Seville until all organised football was indefinitely postponed in March as COVID-19 swept Spain.
LaLiga: Joao Felix marks return from injury with goal to help Atletico Madrid beat Villarreal; Alaves best Athletic Bilbao
Substitute Joao Felix returned from injury and scored his first goal in more than two months to help Atletico Madrid get back in the fight for a Champions League berth on Sunday.
Former Barcelona coach Ernesto Valverde says his next job could take him 'off the beaten track', to Australia or Japan
'A career in football does not last forever and sometimes you think you have to take the opportunity to live in strange places', said Valverde
Copa del Rey: Iker Muniain's goal gives Athletic Bilbao slight edge over Granada with narrow victory in semi-final first leg
Athletic spurned early chances before the electric Williams broke down the left flank and drove a low ball across for Muniain to convert from close range.
Copa del Rey: Revamped tournament earns praise from fans, players and small clubs after upsets of heavyweights
The transformation of the Copa del Rey, however, has earned rave reviews from fans and players, above all from the mid-level and small clubs which now have a much better chance to pull off an upset.