in 2017 Born in
América,
Buenos Aires Province, Ustari arrived in
Independiente's youth system at the age of 14. The untimely deaths of Emiliano Molina and
Lucas Molina – both playing in his position – propelled him to the first team sooner than expected, and he made his
Primera División debut on 5 October 2005 in a 2–0 win against
Newell's Old Boys, remaining first choice with the
Avellaneda side in the following tournaments, under both
Jorge Burruchaga and
Miguel Ángel Santoro (both former players with the club, the latter also a goalkeeper). On 10 June 2007, Ustari scored from a
penalty kick against
Quilmes, also leaving the pitch injured and going on to miss
the year's
Copa América. One month later, he signed for
Getafe in Spain for
€4 million, teaming up with his compatriot and goalkeeper
Roberto Abbondanzieri. His official debut came on 26 September 2007, in a 2–1
La Liga loss at
Valencia. He was first-choice in their
runner-up run in the
Copa del Rey, including in the
3–1 final defeat against the same opposition. Ustari struggled during his spell in
Madrid, due to inconsistent performances and several injury problems. On 17 July 2012, following a 14-month lay-off due to the latter, he terminated his contract which still had another year running. On 25 July 2012, Ustari returned to his country and joined
Boca Juniors. He moved back to Spain one year later, however, with
Almería which had just
returned to the top flight. On 21 January 2014, after only four
Copa del Rey matches to his credit, Ustari was released by the
Andalusians and signed a six-month contract with
Sunderland. He made his debut for his new team four days later, keeping a
clean sheet in a 1–0 home win over
Kidderminster Harriers in the
fourth round of the
FA Cup. He was also in goal in the following game in the tournament, and the result was the same against
Southampton, and was an unused substitute on 2 March in the
final loss to
Manchester City at
Wembley Stadium. On 6 July 2014, Ustari returned to his homeland again to play for
Newell's Old Boys, agreeing to a one-and-a-half-year deal. On 16 December of the following year, he switched to the Mexican
Liga MX after signing for
Atlas. On 2 November 2017, in the dying minutes of the 1–1 home draw with
Tigres UANL while at the service of the latter club, he suffered an horrific injury to his left knee after kicking a long ball forward, going on to be sidelined for nearly two years. Ustari took his game to the
Uruguayan Primera División in July 2019, with the
free agent signing with
Liverpool Montevideo. He subsequently represented
Pachuca in the Mexican top division,
Audax Italiano of
Chilean Primera División and
Major League Soccer's
Inter Miami. Ustari was the undisputed starter for Pachuca throughout the vast majority of his spell, where he won the
2022 Apertura and was also awarded
captaincy. At Inter, he became first-choice at the start of the
2025 season over
Drake Callender. In the opening match of the
2025 FIFA Club World Cup against
Al Ahly, Ustari produced a number of saves, including a penalty from
Trézéguet, in a goalless draw; manager
Javier Mascherano praised his performance afterwards, saying: "Oscar kept us alive in the first half, not just on the penalty kick but two or three other great saves". ==International career==