Wigan boss Steve Bruce believed poor defending cost his team in their 4-1 defeat to Bolton.
Just like against Manchester City last week, the Latics fell behind to an early goal when defender Paul Scharner headed into his own goal in the third minutes when under no pressure.
Wigan equalised 11 minutes later thanks to a great strike by Denny Landzaat, but then conceded goals to Kevin Nolan, Kevin Davies and Nicolas Anelka.
When asked if the 4-1 defeat was tough to take after all the effort his team had put in, Bruce said: "It is tough to take but we didn't really do for me the basic defending what you should do.
"We know that Bolton are going to put it in your box. It was imperative that we started the game well and unfortunately, like we did last week, we've given ourselves a mountain to climb even after just two or three minutes with the goal we've conceded very early again."
Bruce believed his team needed to score when they put Bolton under tremendous pressure after the break when they went in search of the equaliser.
He said: "I think that was the difference in the teams. We didn't defend well enough. We gifted them goals. Bolton have hung in there. The goalkeeper has made a couple of great saves at crucial times. We needed to score in that 20 minutes after half time and we didn't.
"Unfortunately they have gone up the other end and we haven't defended a free-kick good enough again and the game's gone."
He added: "We have to defend better than that, as a group and as a unit and as a team and with the fight we are in and the relegation battle that is what we need to do."
As regards Heskey's substitution in the 72nd minute, Bruce said: "He's obviously been out for ten weeks. It's obviously a big concern that he keeps getting these little niggles but we don't think it's anything too serious, that's for sure."
When Heskey came off, Bruce did not have a recognised striker on the bench because of injuries.
He reflected: "There is not many options in that department unfortunately but we will have to battle through it - everybody else gets injuries and suspensions and what have you, it is how you cope with that."
He thought the partnership of Heskey and Marcus Bent in the first half was terrific.
"Especially in the first half, they led the line very well. But they must be feeling like they're bashing their heads against a brick wall at the moment because any team that goes in our box then unfortunately we look vulnerable.
"So we will have to improve on that - we have got a big job ahead but I knew it was going to be difficult when I took the job so we are ready for the challenge."
When asked about possible activity in the January transfer window, the Wigan boss added: "I have only been in for two weeks. We will assess the players very, very quickly if we possibly can and, of course, if we can make an addition, absolutely fine."