In the 85th minute the highly-rated Vietto took on a sharp pass from Mauro Camoranesi to race clear on Diego Pozo and cleverly lift the ball over the goalkeeper, to earn a 1-0 victory.
The three points lifted Racing Club one point ahead of Newell's Old Boys, who take on Belgrano on Sunday.
Estudiantes were 2-1 winners at home against Quilmes after a dramatic conclusion.
Roman Martinez scored a fine opening goal in the 63rd minute for Estudiantes, sidefooting a shot from the edge of the penalty area into the top right corner.
Quilmes levelled through Martin Cauteruccio after 84 minutes when he found space to lash a left-footed strike across goal and beyond Justo Villar.
But substitute Duvan Zapata cracked in the winner from close range after two minutes of stoppage time when Emanuel Tripodi could only parry a shot from a corner.
San Lorenzo and Arsenal Sarandi battled out a goalless draw, while Humberto Osorio got both for San Martin San Juan in their 2-1 home victory over All Boys, who had opened the scoring when Mauro Matos netted in the 45th minute.
The host side had Christian Alvarez sent off four minutes into the second half but Osorio headed a 57th-minute equaliser and then fired in the winner after 72 minutes.