And the striker has vowed to repay his old Rangers team- mate by netting in the crucial showdown with Macedonia tomorrow night.
McGregor denied Dusan Tadic of Serbia in the final minute of the national team's opening Group A match at Hampden.
The stunning block ensured Craig Levein's side picked up a precious point from their meeting with Sinisa Mihaijlovic's team.
Miller, now playing for MLS club Vancouver Whitecaps in Canada, feels Scotland still have every chance of reaching Brazil in two years' time.
And the 32-year-old is hoping they can kick-start their qualifying campaign with an outright victory against Macedonia tomorrow evening.
He reflected: "We created a lot of chances against Serbia and had a couple of decent opportunities to score. It was disappointing not to. But, at the same time, we could have lost it at the death.
"Big Greegsy produced a save from what was arguably the best chance of the game. If that lad had put the ball past him and we had come away from Hampden on Saturday with a defeat then everybody would have been devastated.
"Everybody would have been saying to us: 'The campaign is finished! You have no chance of getting to the World Cup!'
"Fortunately, he saved it, we got a point and, in my opinion, a good result. If we can get three valuable points against Macedonia we will have made a decent start."
Miller added: "Greegsy is a top, top goalkeeper. Simple as that. He proved it against Serbia once again. Not that he needed to. The saves he made in the first half were ones you would expect him to make. But the one he made late on was superb. It was a big, big save to make."
Miller, who won his 61st cap in the 0-0 draw with Serbia, feels Scotland defended well in their opening World Cup qualifier. And the hitman reckons if the national team can improve their play in the final third they can take all three points tomorrow evening.
He said: "We defended very, very well at the weekend. Andy Webster and Christophe Berra were outstanding in the centre of the backline.
"For somebody making his debut, Paul Dixon did very well at left-back as well. We kept a clean sheet against a very good team.
"Things didn't fall for us up front on Saturday. Either that or our final pass wasn't good enough. But that happens. We can only build on that and get better in that area."
Miller was unaffected when the Tartan Army started chanting the name of Jordan Rhodes, who had been left on the bench by Levein, in the second half against Serbia.
Rhodes is one of the hottest properties in British football and scored a superb header on his first start for Scotland against Australia at Easter Road last month. The Blackburn Rovers striker came on with QPR star Jamie Mackie with 10 minutes remaining and was unable to make a difference.
Miller revealed he thought his replacement had won the game in stoppage time – and backed him to net if he is given an oppor-tunity to play tomorrow.
He said: "When I went off with 10 minutes to go and Jordan went on I was hoping it was going to be the dream Hampden debut for him. It nearly was!
"The Serbian keeper parried James Forrest's shot in stoppage time and I thought Jordan would be right there to tap it in. There were a few situations like that against Serbia.
"You'd have to be living in a cave not to know about Jordan. His record in the last year has been phenomenal. He has scored a lot of goals.
"To score 41 goals in a season, as Jordan did at Huddersfield, is an incredible return for anyone at any level. He marked his first start against Australia last month with a goal.
"He has a lot of experience as well for somebody so young. He has played in the first team at Huddersfield for a few seasons. I am so happy we have got him with us in the squad for this campaign."
Miller feels more chances will fall Scotland's way against Macedonia with Barclays Premier League players Steven Naismith, James Morrison and Robert Snodgrass all involved in the squad. And he has promised that, next time around, their endeavours behind him will not be in vain.
He stressed: "There is a lot of invention in the squad. Look at the team we started with on Saturday. We had Naisy, Mozza and Snoddy. They are all attacking players. Charlie is also fond of getting forward as well.
"We have a lot of attacking options. We were disappointed not to take advantage of a few situations we created at the weekend. We got the ball in good areas and the final pass or shot wasn't quite right. Hopefully, that will change."