Cesar Azpilicueta claims Chelsea "deserved more" from their trip to Old Trafford to face Manchester United on Sunday, but feels the team will "come back stronger" after the defeat.
The final scoreline flattered Ole Gunnar Solskjaer's side, however, after a first-half which saw the visitors hit the woodwork twice and squander a number of other good chances.
Frank Lampard's men started brilliantly, but Kurt Zouma's clumsy challenge on Rashford around the 20-minute mark allowed the hosts to take the lead from the penalty spot.
Chelsea continued to edge the contest thereafter, but when Martial added a second 65 minutes in, the momentum completely swung in United's favour.
Rashford's second came two minutes later, as he produced a superb finish after latching onto a pinpoint Paul Pogba pass, before James rounded off the scoring late on.
Azpilicueta has admitted the result is "tough to take" for Chelsea, who suffered their heaviest loss against United in the league for 54 years.
"We’re obviously very disappointed with the result because we controlled the game, especially in the first half, and created a lot of chances but we couldn’t score," Azpilicueta told Chelsea's official website.
"It’s a tough scoreline to take but we weren’t clinical in the boxes and after we conceded two goals in two minutes, things were more difficult for us.
"From that point, we were more open and gave them more spaces, they got more confidence and at the end, we got a tough result. We deserved more but it is what it is and we have to move on."
Lampard raised a few eyebrows before the match by including Mason Mount and Tammy Abraham in his starting line up, both of whom spent the 2018-19 season playing in the Championship.
Olivier Giroud and £58 million ($70m) signing Christian Pulisic were left on the bench and had to be content with late cameos against United.
Azpilicueta went on to defend Lampard's selection, insisting the younger members of Chelsea's squad will end up making a huge contribution to the campaign.
"We trust in them and they are here because they deserve to be here," he added. "They are fighting in every training session and now we have a massive opportunity to create a fantastic group.
"Everyone would like to start the season in a better way but we have to learn from every game and come back stronger."
Chelsea are back in action against Liverpool in the UEFA Super Cup on Wednesday, before hosting Leicester in their next league game four days later.