The Mali striker played winger Jesus Navas through on the right in the ninth minute and surged into the penalty area to pick up the Spain international's low cross and smash the ball into the roof of the net.
French defender Gregory prevented Navas from doubling the visitors' lead with a goal-line clearance on the quarter hour and Ndri Romaric clipped a post with a header shortly after.
Sevilla moved two points clear of Valencia, who were beaten 3-2 by visiting Real Madrid on Saturday thanks to a double from Real's Argentina striker Gonzalo Higuain.
Real's win was soured by a serious knee injury to defender Pepe that will keep him out for six months.
Barca, who have played one more game than all their rivals, have 39 points from 15 matches, five ahead of Real. Sevilla are four points further back on 30 and Valencia have 28.
COOL FINISH
Reyes took a nasty-looking tumble over Lopez late in the second half, landing awkwardly on his head, and was stretchered from the pitch wearing a neck brace, before striker Llorente met Damian Escudero's cross to grab the three points.
"We hadn't won away from home yet this season and we are very happy because it's a victory that could set us on our way up the standings," Villarreal coach Ernesto Valverde said at a news conference.
Valverde's side climbed to 10th and Atletico remain in 14th with just 13 points from their 14 matches.
Almeria's Nigerian forward Kalu Uche rose unmarked to nod Michel's cross past Daniel Aranzubia in the 58th minute before Pablo Alvarez headed Depor's equaliser with around a quarter of an hour remaining.
