Lionel Messi recovered from a flu quicker than Barcelona expected and netted a brace as a substitute in a 4-0 win over Osasuna in the first leg of their Copa del Rey series on Wednesday.With Messi starting on the bench and David Villa out with a broken leg, Cesc Fabregas launched the rout by scoring off passes from Xavi Hernandez in the 14th and 19th minutes to take his goal tally to 13 goals in all competitions this season.Messi, who was a last-minute inclusion in the squad, went on after halftime.Showing no signs of illness, Messi headed in Fabregas' cross in the 72nd and capped the win in stoppage time."They first said Messi had a fever and was going home, (then) he comes out and scores two goals. What can we do?" said Osasuna coach Jose Mendilibar, whose team entered the night undefeated in its last seven matches. "It would be a miracle to make it to the next round now. We are going to forget about the Copa and focus on the league."Even though earlier in the day Barcelona had said Messi would miss the match because of the flu, he was included after "responding well to treatment," according to the club.Barcelona's latest win added to its more than impressive numbers on the season.Pep Guardiola's team has outscored opponents 37-1 in eight straight victories since losing 1-0 at Getafe and hasn't conceded a goal in 12 straight home games while scoring 53 times."A 4-0 win is an excellent result," Guardiola said. "But the knockout series is not over. We have to go to Pamplona and play for 90 more minutes."Pedro Rodriguez and young winger Isaac Cuenca accompanied Fabregas in attack, and Guardiola opted to deploy a three-man defensive line that freed Dani Alves to play on the right flank.The speedy Brazil defender had the hosts' first shot six minutes in and provided a constant threat throughout.Osasuna came out pressing far up the pitch despite recent memories of the 8-0 rout it suffered in its first visit to Camp Nou in league play earlier this season.But Barcelona's possession-based passing game soon pushed the visitors into their own area and crushed any thoughts of a surprise.The European champions broke through when Xavi completed a great team buildup by finding the unmarked Fabregas on the left side of the area to slot by Osasuna goalkeeper Asier Riesgo.The two Spanish internationals combined again shortly after as Fabregas took a pass from Xavi inside the edge of the area, turned to lose a defender, and beat the oncoming Riesgo with an exquisite chip shot to double the lead.Messi went on for Pedro to the cheers of the home fans in the 59th and saw his chip try bounce wide after Alves played him through the defense. But Riesgo could only look on when Messi rose up to redirect Fabregas' pass into the back of the net minutes later.The Argentina forward finished off the rout late when he took Xavi's pass and fired in a left-footer for his 31st goal of the season in all competitions."I think we played well in our passing game with and without Leo," said Guardiola. "But the final 15 yards before the net, that is another game, and in the last 15 yards there is nobody like Leo."Barcelona will meet Real Madrid in a rematch of last year's final in the quarterfinals if both teams win their last 16 ties.Earlier, Imanol Agirretxe scored one goal and set up another to lead Real Sociedad to a 2-0 win over Mallorca.On Tuesday, defending champion Madrid staged a second-half comeback to edge Malaga 3-2, while three other top-flight teams failed to beat lower-division opponents. Third-division Mirandes beat Racing Santander 2-0, second-division Alcorcon downed Levante 2-1, and third-tier Albacete drew 0-0 with Athletic Bilbao.Valencia hosts Sevilla while Espanyol visits Cordoba on Thursday.The second legs of the round of 16 will be played next week