UEFA.com's Chelsea FC match reporter Trevor Haylett reflects on their round of 16 exit, pondering Diego Costa's statistics and Gary Cahill's words on the treble-chasers' fatigue.
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Why does Diego Costa struggle to make an impact in the UEFA Champions League? Compared with the Premier League where he leaves defenders licking their wounds after coming off second best, his impact in the competition this season has been limited.
The bare statistics tell a startling story for the 26-year-old Spain forward: 21 appearances in the domestic league, 17 goals; seven UEFA Champions League appearances, 0 goals. In the Premier League he tallies 2.4 shots per game, in Europe it's been 1.7, with 68% domestic shooting accuracy compared with 50% in the run ended by Paris Saint-Germain in the round of 16.
He was a success in Club Atlético de Madrid's journey to last year's final but it just hasn't happened for him this time round. Maybe it is because his buccaneering, aggressive style doesn't work so well when faced with defenders who are more experienced on the European stage.
Whatever the reason, it is something José Mourinho will look to rectify next term if the problem has not righted itself. He can't afford to have his main marksman struggling to make his presence felt.
That said, it may well be that Chelsea's pursuit of trophies on all fronts finally caught up with them at Stamford Bridge on Wednesday. Indeed defender Gary Cahill admitted that they lacked urgency.
Mourinho had highlighted the difficulties English sides face compared with their continental colleagues, entering the European arena straight from a typically fearsome contest in the Premier League. In their 43rd fixture of the campaign there were signs of fatigue in the second half as League Cup winners and Premier League leaders Chelsea strained to make their numerical advantage count.
"We certainly weren't cautious," said Cahill, "but we just didn't play very well compared to what we are used to at home. We seemed to lack a bit of urgency and we weren't at our best. When you are not at your best it is very difficult to win, whether the team against you has ten or 11 men.
"We will sit down tomorrow on reflect on the reasons why we couldn't get hold of the game, especially in the second half. After the red card we thought we could go on from there but credit to Paris Saint-Germain, they did very well with ten men."