Atletico Madrid s Luis Suarez, left, scores his side s second goal during the La Liga soccer match between Atletico Madrid and Barcelona at the Estadio Wanda Metropolitano in Madrid, Saturday, Oct. 2, 2021. AP
Lemar struck the opener from a pass by Suarez in the 23rd minute. The France forward returned the assist for Suarez to score his first goal against his former club in the 44th.
Barcelona's defeat came hours after club president Joan Laporta broke his silence and pledged that Koeman would stay on regardless of the result at the defending Spanish league champion. His defense of Koeman came after days of reports in the Spanish media that Laporta was ready to replace him after Barcelona lost its first two Champions League games by the combined score of 6-0.
Koeman watched his team's latest demise from a box in the Wanda Metropolitano stands, where he served the second of a two-game ban for protesting the refereeing in a draw at Cadiz.
The first goal by Lemar caused Koeman to throw up his hands. After Suarez's second, he could only rub his eyes before he picked up his phone to presumably give more orders to assistant Alfred Schreuder in the dugout.
Schreuder made substitutes in the second half, but Diego Simeone's experienced team had no trouble locking down the three points.
Simeone led the crowd of more than 60,000 in celebrations during the final minutes of Atletico's first match with attendance back at full capacity since the start of the pandemic. Health authorities lifted the nationwide cap of 60% attendance this week.
Atletico moved into second place, level on points with leader Real Madrid before its game at Espanyol on Sunday.
Barcelona is in ninth place at five points behind the top two. Koeman's side has only won three of nine matches in all competitions this season, its first without Messi in nearly two decades.