I never understand these arguments about what a player "should" be able to do because they get paid a fortune or whatever. The reality is that they can't. When a cyclist is cycling for 7 hours a day, he's up against other cyclists who are all doing the same. When a football team plays within 3 days, it's often (not yesterday, admittedly) against a team who last played 7 days ago. In the same way, when a tennis player goes through one of those mammoth 6 hour tennis matches, they don't tend to do very well in the next round.
Yesterday wasn't anything to do with that though. I always worry when we don't have one of Bernardo or Gundogan in midfield, because they're the sort of players that don't give the ball away and allow us to build attacks. Take Mahrez out as well and you're losing three players who you can rely on to pass it to in any situation and they'll control it. KDB and Sterling are great players (when on form), but they aren't exactly strangers to giving the ball away. And that's fine normally, because we had a good mix, but yesterday until Phil came on, we didn't have anyone who is like that. Gundogan also made a massive difference.
But the lack of substitutions suggested to me that Pep didn't consider it a priority. Sure, nice to win, but if the team he put out on the pitch couldn't win it, he wasn't going to risk more players getting injured or tired.