London: Jose Mourinho showed the kind of decision making that once took FC Porto to the Champions League title. On Tuesday, it gave Chelsea a 2-1 win over his former team and a place in the quarterfinals of the Champions League at the expense of the 2004 champions. Michael Ballack scored with a left-foot half volley in the 79th minute to complete a comeback and give the English champions a 3-2 aggregate win. Chelsea had dominated possession and chances in the first half but trailed after a 14th-minute goal by winger Ricardo Quaresma. Mourinho had seen enough and decided to increase the tempo further. He brought on attacking midfielder John Obi Mikel at halftime in place of defensive midfielder Claude Makelele. Chelsea, which drew 1-1 in the first leg in Portugal two weeks ago, got an equalizer from Arjen Robben three minutes after the switch. "We were playing well in the first half," Porto coach Manuel Jesualdo Ferreira said. "But then came a change by the Chelsea team." Mourinho, who also led Porto to the UEFA Cup as well as Champions League before joining Chelsea in 2004, was in no doubt that it was his halftime talk and change that led to Chelsea's improvement. After all, he is the manager who has referred to himself as "The Special One." "I just made them think a little bit," Mourinho said. "I told them, 'At the moment we are out of this competition. We either enjoy it or are scared of it.' "I think at times it is possible to enjoy this kind of moment." Chelsea had its first chance at Stamford Bridge through Andriy Shevchenko, who curled a first-minute shot over the bar. However, Porto went ahead on the night and on aggregate in the 14th. Lucho Gonzalez passed from the halfway line and, with Chelsea's defense appealing for offsides, Quaresma took the ball and slipped a shot under goalkeeper Petr Cech with the outside of his right boot. The Blues, who had also trailed in the first game, rallied and created a string of chances. Drogbaas miss Didier Drogba, Africa's player of the year and one of the Champions League's leading scorers this season, had a chance for his sixth goal in the competition when Ashley Cole stole the ball and crossed from the left. Drogba initially let the ball run to Shevchenko, who had a shot blocked, and Drogba, under pressure from a defender, put the rebound high and wide. Ballack missed the ball as he tried to shoot in the area and Frank Lampard shot straight at goalkeeper Helton as he ran in on Shevchenko's cross from the left. "I don't know how many attempts at goal there were by Chelsea," Jesualdo Ferreira said. "They have a method of playing that produces results _ the kind of result you saw tonight." As Chelsea tried to force a goal before halftime, Robben was booked for diving under a challenge by right back Fucile in an attempt to win a penalty. Lampard was also warned, but not booked, by referee Roberto Rosetti for falling too easily under a challenge just outside the area. Spurred by Mourinho's halftime talk, Robben collected a pass from the right and cut inside onto his left foot before hitting a 25-meter (yard) shot at Helton. The goalkeeper only got his hands rather than his whole body behind what seemed an innocuous shot and the ball spun up over him into the net. Mourinho refused to blame Helton for the error. "The way we played, if we didn't score in the 48th, we score in 49," Mourinho said. Stung by Chelsea's response, the Porto coach took off right back Marek Cech and midfielder Raul Meireles and brought on striker Adriano and central midfielder Ibson as substitutes. Chelsea, however, continued to dominate, with Lampard hitting a free kick into the wall and substitute Paulo Ferreira heading over shortly after from close range. Chelsea then peppered Porto's area with crosses, trying to force another mistake from the goalkeeper. "We played with a higher intensity because the English league gives us that intensity," Mourinho said. A cross from the left that brought the winning goal, taking Chelsea one stage further than last season, when it lost to eventual champion FC Barcelona. Drogba headed a deep cross from the left across goal to Shevchenko and the Ukraine striker nodded the ball to the center of the area where Ballack was ready. Ballack, a runner-up in 2002 with Bayer Leverkusen, adjusted his feet and scored as he fell to the turf. Porto has not reached the quarterfinals of the Champions League since it won the competition under Mourinho.