A second-half strike by forward Armand Lauriente gave Sassuolo a surprise 1-0 win over nine-man Atalanta in Serie A on Saturday, ending the visitors' unbeaten run in the Italian top-flight this calendar year.
Atalanta, who ended January with a 1-0 defeat to Inter in the Coppa Italia quarterfinals, suffered their first Serie A loss since the league resumed after the World Cup break.
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Gian Piero Gasperini's side dropped to sixth in the standings and are level on 38 points with fourth-placed Lazio and AC Milan in fifth, both with a game in hand.
Sassuolo, coming from an impressive 5-2 win over title holders Milan in their last outing, moved up to 15th and increased their cushion above the relegation zone to 10 points.
"We can say that we are healed," Sassuolo midfielder Davide Frattesi told DAZN.
"After Milan we didn't get too excited because one swallow doesn't make a summer, but we needed a couple of important results to say that we are cured.
"The attitude has changed, it's a fundamental thing. We talked about it in the dressing room, something was wrong and we solved it. The quality has always been there, even in the most difficult moments, and that's the most important thing."
Atalanta were left with 10 men just before the half-hour mark when defender Joakim Maehle was sent off for a foul on Sassuolo forward Domenico Berardi, following a VAR review.
Sassuolo took the lead in the 55th minute through Lauriente who unleashed a brilliant long shot from the edge of the box, sending it inside the far post for his fourth goal in his first season in Serie A.
Atalanta midfielder Marten de Roon had a chance to level from a free kick 10 minutes later but Sassuolo goalkeeper Andrea Consigli produced a great save.
Midfielder Nedim Bajrami could have doubled the lead for the hosts with eight minutes remaining in regular time but Atalanta keeper Juan Musso was in the right place to deny his effort.
Atalanta were reduced to nine men in stoppage time when substitute Luis Muriel saw a direct red card for what appeared to be an argument with the referee.
Earlier on Saturday, AS Roma scored twice inside the opening six minutes to win 2-0 at home against 10th-placed Empoli.
Jose Mourinho's side moved to 40 points from 21 games and are third in the standings, level with second-placed Inter who host Milan on Sunday.