Thomas Tuchel had referred to defeat against West Brom, his first since becoming Chelsea coach, as a “slap in the face” and four days later his team might have been hit even harder in Seville. Porto though couldn’t land the punch they kept trying to throw and in the end it was Chelsea who delivered what could well prove the knockout blow, close now to a first Champions League semi-final in seven years. For much of the night Chelsea had held on to a slim lead given to them by Mason Mount’s superb goal after half an hour. And then with four minutes left at the Sánchez-Pizjuán, Ben Chilwell took advantage of Jesús Corona’s dreadful control to dash into the area, across Wilson Manafá, round the goalkeeper Agustín Marchesín and roll the ball into the net to end it. The match and maybe the tie. Porto could barely believe it. A 2-0 defeat would have been painful enough anyway, but this was at “home”, and for much of the night they had played like they were too, on the front foot and racking up more than a dozen attempts on Chelsea’s goal. There was no reward, just greater punishment, while Chelsea may feel that they largely defended well, César Azpilicueta in particular. Porto occupied the right-hand dugout, a modest “Campeão” (Champions) banner was stretched across the south end, a couple of bars of their anthem were played before Tony Britten took over, and of course they wore blue and white. Chelsea appeared in the same pink kit they wore here on Olivier Giroud’s grand night against Sevilla. But the most significant thing about Porto being the home team was of course that when Chelsea scored just after the half-hour it carried the extra weight of an away goal. It was a fine strike too, Chelsea stepping beyond the pressure to which they had been subjected until then and Jorginho finding Mount by the right corner of the area. With Zaidu Sanusi drawn in, he turned superbly, spinning beyond the defender with one smooth touch, and hit the ball hard and low in by the far post beyond Marchesín. That hurt. Already considered the weakest team left in the competition, the absence of Sérgio Oliveira and Mehdi Taremi deepened that assumption and so too did a comically bad early free-kick routine. Yet what followed made a lie of that, even if as time passed it was hard to avoid the conclusion that Porto lack something of what Chelsea have in abundance: a certain knowhow, efficiency and decision. Talent, too. Both goals were testimony to that. With Otávio and Corona going at Chelsea, Zaidu coming from deep and Mateus Uribe appearing in and around the area, Porto certainly made sufficient chances to have led before they trailed. First Luis Díaz saw a shot blocked by Andreas Christensen, then Uribe’s volley skimmed the top of the netting and a moment later Zaidu slipped as he was preparing to deliver, deep in Chelsea’s area. Édouard Mendy then pushed out Otávio’s corner, curling in under the crossbar, only to see Pepe head to Zaidu who somehow volleyed over from close range. Chelsea had escaped then, a moment later when Mateo Kovacic had to prevent Díaz dashing clear, and again when the ball got caught under Otávio’s feet as he combined with Manafá and got free in the area. Even after Mount had scored, Porto kept pressing, Azpilicueta reaching to deflect wide from Corona and Mendy saving Pepe’s header. Next Uribe, all quick footwork, dribbled through but found Antonio Rüdiger closing down the shot. At half-time it was 8-1 in shots to Porto but 0-1 on the scoreboard. When Chelsea worked a chance for Timo Werner at the start of the second half it was almost the first time he had been seen, and it didn’t signal a shift. Porto still carried the weight of the game. A lovely Manafá pass curled through the right channel to put Moussa Marega through but his shot was saved by Mendy. And a clever angled ball from Corona found Díaz heading towards goal, but Azpilicueta was across quickly. And then Díaz’s shot bent just wide. Soon Chelsea had to scramble off the line, although the referee had spotted a foul first. Next Marega couldn’t get a clean enough connection on the turn and then he tumbled under a challenge from Azpilicueta, the penalty shouts greater than Porto’s belief that it really was. Those were borne perhaps of frustration and the realisation that they lacked a little quality and clarity. Which is natural enough when arguably your best two attackers are absent. That was illustrated again when Díaz couldn’t control in the Chelsea area and, even more cruelly, when nor could Corona on the edge of his own. Chilwell was away to hand Chelsea a huge lead to take into the second leg on Tuesday: same time, same place.