The Steelmen recovered from the early concession of a goal to Aberdeen’s Christian Ramirez to book a last eight home clash against Hibs thanks to first half strikes by Kevin van Veen and Connor Shields.
Backed by a vociferous home crowd, ’Well helped ease the pain of a disappointing start to the year which had seen the only victory in their previous seven games being a 2-1 extra time success over Championship side Greenock Morton in the cup’s fourth round.
"That was a win for our personality and character,” Alexander said. “We have had a difficult month and we went down 1-0 at home after two minutes.
"We have spoken about personality and character. We showed it.
"Everybody showed it and they were all brilliant. If the outfield players didn't get to the ball, Kelly did.
"It was a tough game and the conditions at the start of the game were horrendous.
"We were disappointed to go 1-0 down in a couple of minutes. We didn't cope with the conditions in the first 15 minutes.
"But as soon as my players understood what it took to win this game, they were brilliant.
"We got ahead at half-time which has been a rarity for us. We took advantage and we could have won the game by more as we had some real good chances."
’Well were under the cosh in the closing stage against the Dons – who sacked manager Stephen Glass in the wake of this defeat – but booked a quarter-final tie at home to Hibernian on the weekend of Saturday, March 12 thanks to a wonderful one handed save by Kelly from Ramirez’s shot at the death.
Alexander said: "I had a chat with Liam the other day. It's been really difficult for him in the last month as he hasn't had too many saves to make when we've been beat.
"We spoke about focus when you haven't got much to do in games. You have to be ready and the top ones are. That would have been harsh on us as we should have been further ahead.
"It's a brilliant save but we know about the saves Liam can make."