RIO DE JANEIRO (AFP) - Tennis world No. 1 Rafael Nadal breezed into the quarter-finals of the ATP Rio Open on Thursday, but admitted afterwards that he was still feeling the effects of a back injury.

Nadal, in his first event since losing last month's Australian Open final, needed only 74 minutes to rout Spanish compatriot Albert Montanes 6-1, 6-2 and book a date against Portugal's 48th-ranked Joao Sousa, who eliminated 87th-rated Spaniard Albert Ramos 7-6 (8-6), 2-6, 6-3.

Nadal wore elastic tape across his lower back during the match and said the injury he suffered in losing the championship match at Melbourne to Stanislas Wawrinka still nags him.

"When you get injured in the final of a Grand Slam and stop for two-and-a-half weeks, it is not easy to come back," he said. "The back is still bothering me a little bit but I am happy with my decision to be here."

Nadal broke Montanes three times in each set and won the final four games of the match as he improved to 3-0 all-time against his compatriot, having yet to lose more than three games in any set against him.

The sore back forced the 13-time Grand Slam champion to skip Buenos Aires last week, leaving his return for Rio, where he starts a clay-court season that he hopes will culminate in a ninth career French Open crown.

Nadal, who reached a career-high 14 finals last year, seeks a berth in his third consecutive final, having won at Doha in the first week of the year.