The 21-year old required only an hour and 12 minutes to dismiss his opponent 6-2 6-3, breaking Andujar on three occasions.
Ruud has some impressive wins in his pocket already this season, defeating both Italy's Fabio Fognini and American John Isner at the ATP Cup in January.
With victories over two Top 20 players this year, Ruud is hoping to win his maiden ATP Tour-level title this week in Buenos Aires. The eighth seed next faces either defending champion Marco Cecchinato or World No.88 Roberto Carballes Baena.
Clay-court specialist Pablo Cuevas defeated Italy's Lorenzo Sonego 6-4 6-4 in an hour and 38 minutes. The Uruguayan faces the winner between seventh seed Albert Ramos Vinolas of Spain or Argentine Leonardo Mayer.
Thiago Monteiro overcame Spaniard Jaume Munar 6-3 6-3 in an hour and 42 minutes. The Brazilian was pushed by the 22-year old Munar, saving 10 of 11 break points. Monteiro will meet fourth seed Borna Coric for a spot in the quarterfinals.
Argentine Federico Delbonis fought past Bolivian Hugo Dellien 1-6 6-3 7-5 in a two hour slugfest. It will be a battle between home favorites as he faces compatriot Diego Schwartzman in the second round. The top seed is coming off a disappointing loss to Chilean Cristian Garin in the Cordoba Open final.
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