David Houghton believes Ashley Giles has to maintain the form he demonstrated in the second Test at Edgbaston if England are to win the Ashes for the first time in 18 years.
Houghton had questioned whether Giles should be part of the team after his showing in the opening Test at Lord's when he bowled just 11 overs.
It meant that a greater workload was placed on strike bowlers Steve Harmison and Andrew Flintoff as Australia won by 239 runs.
But Giles was back to his best on his home ground in Birmingham, keeping the batsmen under control and also picking up five wickets.
Houghton, Derbyshire's coach, said: "Ashley did the job really well at Edgbaston that he needs to do for the England seam attack to operate. He is an integral part of the team. His role is vital to the seamers because he has to bowl an end tightly and if he can pick up a wicket or two, that's fantastic.
"But he has to bowl long periods, and bowl tightly, so the seamers can rest. That's what he has done effectively for the last two or three years.
"No-one expects him to get the figures that Shane Warne gets. He has a job to do which balances the success of a seam attack. In the first Test he didn't do that. In the second he did."
Houghton insisted his opinions on Giles' performances at Lord's were misrepresented and led to him coming under fire from the Warwickshire spinner.
He said: "If Ashley is still worried about the criticism I gave him, what a great way to answer!
"I've known Ashley since he was 17. He is a good mate. I'm not sure if he will class me as a good mate anymore after all that rubbish which was reported. It is totally unfair. Since then I have just copped flak from everywhere.
"I texted him and tried to explain. I've heard nothing and every time he got in front of the television or in the papers, he has slagged me off. He is quite entitled. I would have reacted the same.
"All I was trying to do was give an opinion of how England would win the next Test and the series after losing at Lord's and how important his role is and therefore, if he is not doing his role, then he shouldn't be playing.
"But, if he can continues to do that role well, it makes the balance of the bowling attack absolutely correct."
Houghton, who also had a spell as coach at Worcestershire, had predicted before the series that England would win 3-1 and his belief is unaltered.
He said: "I still believe England are going to win the series 3-1. I believed that from the start of the series and I still do.
"I don't think they would have come back from 2-0 but now they have crossed that winning line against Australia and that's a big bridge
to cross. England are definitely better. England cop stuff of the Australian bowlers but now they can dish it out even better."
Giles, meanwhile, has claimed England's players would have been "strung up" had lost the Edgbaston Test.
Giles commented: "We knew what it meant to us and we knew what it meant to everybody else.
"It's fine lines because we were three runs away from being sent to the moon again as well. We'd have been strung up if Australia had won so we're just happy it ended this way."
Giles took five wickets in the match and was pleased with his performance after a difficult week.
He now hopes to maintain the momentum at Old Trafford but is unconcerned if the pitch does not favour his spin as that could help nullify Australia's Shane Warne as well.
"I've had a tremendous amount of support from my wife Stine and the family and it was nice that they could be there.
"It's great because the stuff that goes around hurts them as much as it hurts me so I owe a lot to them.
"Old Trafford traditionally takes spin but I'm not bothered if it doesn't. It's about what is best for the team." n Australia have called up Middlesex overseas seamer Stuart Clark to boost their bowling options.
Glenn McGrath is already ruled out of the third Test, while Brett Lee is rated at no more than 50-50 after being hospitalised with an infection in his left knee.
With doubts over their two leading seamers, Australia called up Clark, who made his first appearance of the season in Middlesex's defeat to Warwickshire last week. Clark bowled very well in his opening spell, but looked some way short of full match fitness and lost effectiveness as the game progressed.