Bastia surges up Ligue 1 table
Midfielder Ryad Boudebouz scored in the sixth minute and hit the crossbar with a curling shot midway through the first half as Bastia dominated.
The home side did not have to wait long for the second goal as Wahbi Khazri scored from the penalty spot in the 23rd after he was fouled by defender Lamine Gassama.
But midfielder Mathieu Coutadeur pulled one back for the visitors 10 minutes later with a deflected shot, and striker Kevin Monnet-Paquet went close to equalizing moments later.
Former Juventus midfielder Milos Krasic made it 3-1 in the 59th after running onto Gianni Bruno's clever backheel and clipping the ball over goalkeeper Fabien Audard despite a tight angle.
Ivory Coast midfielder Romaric added the fourth near the end when he headed in Boudebouz's cross from the left.
''I'm proud, we played well on every level,'' Bastia center half Sebastien Squillaci said. ''We really wanted to do something for our home fans.''
Lorient midfielder Larry Azouni was sent off with five minutes left for a rough tackle on defender Julian Palmieri, who limped off shortly after and was replaced.
Lorient remains mired in the relegation zone.