BUENOS AIRES, April 27 (Reuters) - Midfielder Diego Buonanotte scored twice to inspire River Plate to a 4-2 win over Argentinos Juniors on Sunday and keep them level with Argentine championship leaders Estudiantes. Boca Juniors lost their unbeaten record in the competition when they were beaten 1-0 at San Lorenzo and dropped to fourth. Buonanotte, 20 and one of Argentina's most promising players, opened his account in the 32nd minute, outfoxing his marker before scoring with a well-placed left-foot shot. Alejandro Delorte equalised before halftime but Buonanotte put River back in front four minutes after the re-start when the 1.60 metre midfielder scored with a deflected long-range shot. Argentinos were level again eight minutes later when Pablo Barzola converted a controversially-awarded penalty. But River regained the lead through Uruguay striker Sebastian Abreu in the 61st minute and Colombian striker Radamel Falcao Garcia completed the scoring in injury time. Estudiantes, who beat Rosario Central 3-1 on Friday, and River both have 27 points from 12 games and a goal difference of 11, but Estudiantes lead on goals scored. South American champions Boca were sunk by a second-minute goal from Juan Mensequez at San Lorenzo, who took advantage as the Boca defence were caught out by a long ball upfield from Aureliano Torres. Boca's misery was complete when midfielder Fabian Vargas was sent off in injury-time for a second bookable offence. San Lorenzo climbed to third with 24 points, changing places with Boca who have one point less.