But victory came at a price for Penney's side as talisman Paul O'Connell picked up an injury in the warm-up that forced him to miss the match with a calf problem and British & Irish Lions scrum half Conor Murray found himself cited after the game.
Murray faces an accusation of 'striking with the elbow', contrary to law 10.4 (a), after the match citing commissioner, Rob Flockhart, issued his report. Glasgow Warriors' replacement scrum half Niko Matawalu also faces a charge of biting.
It was the first time this season the Warriors had not only lost in the PRO12, but also been beaten at home. Defeat came the weekend after they had beaten Exeter Chiefs at Scotstoun in their Heineken Cup campaign.
"I couldn't have asked any more of the lads. It was a really resolute performance at a time when there was bit of adversity, given the adjustments we had to make. So I'm just really proud to beat the best team in the PRO12 at their home ground - it's a great achievement," said Penney.
Penney praised the work of his assistant coaches for bringing out the best in his players defensively as they kept Glasgow tryless throughout, despite a period down to 10 men following Cronin's yellow card and a late, desperate flurry from the home side.
"It was a war of attrition to a degree and it was our defence that won it. Tenacity, desperation, a little bit of detail in terms of understanding how to defend, putting your body on the line and just throwing yourself into it.
"We did that efficiently and I'm really proud of their work ethic and their ability to keep bouncing up and getting in the defensive line."