Barca beat Osasuna 8-0 at home in the La Liga back in September and the Pamplona-based side must have feared another mauling when Cesc Fabregas netted twice in the opening 18 minutes at the Nou Camp – the second a superb chip.
As it was, a strong Barca added two more goals from Lionel Messi, who climbed off the bench to net in the 72nd and 90th minutes.
The Argentinian’s first goal was a close-range header and the second was a fine curling effort from the edge of the box – taking his tally to 31 goals in all competitions this season.
With Madrid fighting back from 2-0 down to beat Malaga 3-2 in their first leg last night, the two Spanish giants remain on course for a repeat of last season’s final – which Jose Mourinho’s side won 1-0 – in the last eight of this season’s competition.
In Wednesday’s other last-16 first leg, Real Sociedad continued their good recent form with a 2-0 home win over Real Mallorca. Sociedad, who have climbed away from the foot of the Primera Division table on the back of five-match unbeaten run, took the lead through Mikel Aranburu in the 17th minute and Imanol Agirretxe added the second nine minutes into the second half.