The league leaders slipped to a 2-1 defeat at lowly Gillingham but only after hitting the woodwork three times late in the second half.
Jason Roberts was the biggest culprit, heading against the post from just two yards out, while Gary Teale and Lee McCulloch also saw efforts come back off the frame.
Victory in Kent would have taken Latics three points clear at the top.
Instead they're locked on 66 points with Sunderland, who moved up to second place after beating Cardiff, and Ipswich, who slipped to third after a surprise home defeat to Queens Park Rangers.
Jewell said: "I suppose I'm being ultra-critical but you can't afford to miss the chances we did at any level of football, let alone Championship level.
"We didn't beat Gillingham because we weren't ruthless enough in front of goal, and at the other end, we couldn't handle their two strikers in the second half.
"We missed some gilt-edged chances and while I'm not pointing the finger at anyone in particular, those chances have to be taken.
"Last week when we beat Leeds at home, we won 11 battles across the park, this time I don't think we won half of them."
The introduction of Gills substitute Mamady Sidibe at half-time was a major factor with the Frenchman setting up Darius Henderson for the hosts' opener eight minutes into the second half.
Nathan Ellington quickly levelled with his fourth goal in as many games, but Henderson hit the winner in the 65th minute.
Jewell said: "Gillingham got the ball forward in the second half and we couldn't deal with their two strikers.
"They were knocking balls over our back four and they looked hungrier than us, which I find hard to believe.
"Gillingham started to outmuscle us and I thought Sidibe did ever so well.
"Give them credit for the way they played and for Stan Ternent for making the change at half-time.
"They're fighting for their lives down at the bottom but we're fighting up at the top to get promoted.
"Promotion is won and lost at places like this and we should at least got a point out of the game.
"When people look at the league table, they would have thought this game would be an away banker.
"But it doesn't work like that, there's no such thing, and this is why this game can drive you crazy at times.
"We have to forget how other clubs have gone on, forget Ipswich lost in midweek and again on Saturday.
"We have to concentrate on getting ourselves over the line because last year we threw it away and we don't want that to happen again."
Jewell added: "It was a smashing goal from the Duke and should have been the platform for us to go on and win the game.
"I really thought we would go on and win it, and even after Gillingham scored again, we went and hit the woodwork three times.
"On reflection, some of the build-up play was good and we got in good situations, but we just weren't ruthless enough.
"We now move on to play Ipswich, a game which will look after itself."
Jewell reported no fresh injury problems, although Alan Mahon missed out for the second game running with a knee injury.
The midfielder will hope to be fit in time to play Ipswich with whom he enjoyed a successful loan last season.
Jason Roberts was the biggest culprit, heading against the post from just two yards out, while Gary Teale and Lee McCulloch also saw efforts come back off the frame.
Victory in Kent would have taken Latics three points clear at the top.
Instead they're locked on 66 points with Sunderland, who moved up to second place after beating Cardiff, and Ipswich, who slipped to third after a surprise home defeat to Queens Park Rangers.
Jewell said: "I suppose I'm being ultra-critical but you can't afford to miss the chances we did at any level of football, let alone Championship level.
"We didn't beat Gillingham because we weren't ruthless enough in front of goal, and at the other end, we couldn't handle their two strikers in the second half.
"We missed some gilt-edged chances and while I'm not pointing the finger at anyone in particular, those chances have to be taken.
"Last week when we beat Leeds at home, we won 11 battles across the park, this time I don't think we won half of them."
The introduction of Gills substitute Mamady Sidibe at half-time was a major factor with the Frenchman setting up Darius Henderson for the hosts' opener eight minutes into the second half.
Nathan Ellington quickly levelled with his fourth goal in as many games, but Henderson hit the winner in the 65th minute.
Jewell said: "Gillingham got the ball forward in the second half and we couldn't deal with their two strikers.
"They were knocking balls over our back four and they looked hungrier than us, which I find hard to believe.
"Gillingham started to outmuscle us and I thought Sidibe did ever so well.
"Give them credit for the way they played and for Stan Ternent for making the change at half-time.
"They're fighting for their lives down at the bottom but we're fighting up at the top to get promoted.
"Promotion is won and lost at places like this and we should at least got a point out of the game.
"When people look at the league table, they would have thought this game would be an away banker.
"But it doesn't work like that, there's no such thing, and this is why this game can drive you crazy at times.
"We have to forget how other clubs have gone on, forget Ipswich lost in midweek and again on Saturday.
"We have to concentrate on getting ourselves over the line because last year we threw it away and we don't want that to happen again."
Jewell added: "It was a smashing goal from the Duke and should have been the platform for us to go on and win the game.
"I really thought we would go on and win it, and even after Gillingham scored again, we went and hit the woodwork three times.
"On reflection, some of the build-up play was good and we got in good situations, but we just weren't ruthless enough.
"We now move on to play Ipswich, a game which will look after itself."
Jewell reported no fresh injury problems, although Alan Mahon missed out for the second game running with a knee injury.
The midfielder will hope to be fit in time to play Ipswich with whom he enjoyed a successful loan last season.