Boselli, who scored for Estudiantes in their 2-1 defeat after extra time by Barcelona in last month's Club World Cup final in Abu Dhabi, struck twice in four minutes in the second half of Friday's match.
For his first, Boselli took a brilliant pass from Jose Sosa, on loan from Bayern Munich, to race past keeper Cristian Campestrini and put Estudiantes two up.
His second for the South American champions was a penalty after Campestrini brought him down four minutes later.
Midfielder Marcelo Carrusca had put the team from La Plata ahead five minutes before halftime in a match dominated by Estudiantes.
Campestrini, who won his second Argentina cap in a 3-2 friendly win over Costa Rica last week, was sent off one minute from time.
Local media reported that Estudiantes must sell Boselli if the offer is for $8 million or more as part of the striker's contract on loan from Boca Juniors. English Premier League club Birmingham have offered between $6.0 and $6.5 million, according to newspapers, and have until Sunday to increase it.
Banfield, whose Apertura championship victory in December was their first league title, are at home to River Plate on Sunday.
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