MANCHESTER — Manchester City forward Sergio Aguero’s last-gasp header secured a 2-1 victory over Bristol City in their League Cup semifinal first leg Tuesday after the second-tier side had frustrated the Premier League leader. City, which has dished out a string of maulings in a stellar league campaign, found the Championship side a tough nut to crack and had to wait until the 92nd minute to grab the winner when Argentine substitute Aguero darted in to head home. The visitors had opened the scoring with a penalty just before halftime after central defender John Stones had fouled Bobby Reid, who dispatched the spot kick with aplomb. Kevin De Bruyne’s equaliser soon after the break turned the tide and City then laid siege to their opponents’ defense in the closing stages before Aguero’s goal gave them a vital advantage ahead of the return leg in two weeks’ time. “My players were fantastic because in football you can win, you can lose, but we try until the end. We win many games in the last minutes because we don’t give up,” City manager Pep Guardiola told Sky Sports. With Manchester City unbeaten domestically all season and streaking clear in the Premier League it was hard to imagine it facing much of a test at home to Lee Johnson’s side, which is 14 points off the pace in the second division. Yet the visitors had beaten four top flight sides en route to the semifinals, including City’s arch rival Manchester United in the last round, and was in no mood to lie down and wait for Guardiola’s City juggernaut to mow it over. Atletico, Valencia in quarters Atletico Madrid booked its place in the quarterfinals of the Copa del Rey Tuesday after seeing off third-tier Lleida, while new signing Luciano Vietto’s hat trick fired Valencia past Las Palmas. Playing in front of a sparsely populated Wanda Metropolitano, it took dominant Atletico until the 57th minute to extend its 4-0 first leg lead, Yannick Carrasco meeting Diego Costa’s cutback and slotting home the opener. Kevin Gameiro tapped in the second 17 minutes later after a neat burst into the box from Angel Correa, and Vitolo made it three nine minutes from the end, racing through and crashing home his first Atletico goal to complete a 7-0 aggregate victory. Argentine forward Vietto ended a long goal drought in spectacular