Oscar Ahumada made his professional debut on 24 November 2002 in a 2-1 win over Olimpo de Bahía Blanca. He played at winning the Clausura 2003 and 2004, only a minor role before moving to Germany moved to VfL Wolfsburg in 2004. There he played along with his compatriots Facundo Quiroga, Andrés D' Alessandro, Juan Carlos Menseguez and Diego Klimowicz. In Wolfsburg, but he completed only four games. In January 2005, he returned to River Plate.
In May 2008 he became very unpopular with the River Plate fans when he said after a game in an interview, "We lost today because we did not have the support of our fans, they are not like the Boca fans. " This statement came after leaving the Copa Libertadores against San Lorenzo de Almagro in the round of 16 Subsequently, the fans demanded the expulsion Ahumadas, but coach Diego Simeone refused this request. Despite the resignation at the Copa Libertadores still had the opportunity to win the Clausura. You fought a head -to-head race with Estudiantes de La Plata, which you could still win in the end. A key role in winning the title had Ahumada and his teammates Ariel Ortega, Juan Pablo Carrizo and a young talent, Diego Buonanotte. In 2010 he moved to Mexico for CD Veracruz. A year later he moved to FK Rostov.
After Ahumada graduated only two league games for Rostov, he moved in 2012 to his home to the CA All Boys.
Ahumada played for the Argentina U-20 National Team, which won the Junior World Cup in 2001. This was held in their own country. He played three games. With 31 years Ahumada made his senior international debut when he came on as a substitute for use in the friendly against Brazil.
- Primera División Clausura 2003, 2004 & 2008
- Junior World Championship 2001