River Plate can overtake both and take top spot in the Clausura standings if they beat Argentinos Juniors at their Monumental stadium on Sunday in a match between the only two teams yet to lose.
Striker Gaston Fernandez put Estudiantes ahead early in the second half when he beat the offside trap to reach defender Leandro Desabato's long, high ball into the box and shot low past goalkeeper Gaston Sessa into the bottom corner.
Argentina winger Enzo Perez scored the second with a penalty in the 83rd minute at a packed Ciudad de La Plata stadium, showpiece of the Copa America in July, where Gimnasia were acting as the home side.
Gimnasia's 37-year-old captain Guillermo Barros-Schelotto, back at his first club after shining for Boca Juniors and Columbus Crew in the MLS, was upset by his team's poor defending.
"We shouldn't be caught out by a punt ahead from 50 metres," Barros-Schelotto told reporters."
Estudiantes coach Eduardo Berizzo said: "We beat 30,000 people [Gimnasia fans]. Winning these kind of matches is very important.
"The team stuck to our game plan and overcame the absence of [injured captain Juan Sebastian] Veron."
Racing raced into a three-goal lead at the "Cilindro" in the suburb of Avellaneda with two goals by inspirational winger Pablo Luguercio and a brilliant third from midfielder Lucas Licht after a one-two with striker Teofilo Gutierrez.
Colombian striker Gutierrez made it four in the first minute of the second half, running onto a through ball from the halfway line to time his chip perfectly over advancing goalkeeper Laureano Tombolini for his third goal in two matches.
But Olimpo, joint top with River last weekend, exposed Racing's defensive frailties with three goals in seven minutes - two by Ezequiel Maggiolo - in a match with a string of chances at both ends.
Maggiolo headed home a free-kick for his first in the 50th minute and struck from eight metres five minutes later with defender Nicolas Bianchi Arce heading in a corner in the 57th.
In four matches played so far this weekend, 18 goals have been scored including Newell's Old Boys' 3-3 draw at home to Huracan in Rosario and San Lorenzo's 3-0 win at All Boys on Friday.
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