In the end they won by five points, but Mayo manager James Horan admitted Down's running game caused his team plenty of bother in the round 2 qualifier in Newry.
Leading by three points at the interval, a goal seven minutes into the second half from Conor Loftus proved to be crucial for Mayo against a Down side that will rue not taking more of their opportunities.
Bouncing back from last month’s disappointing Connacht semi-final defeat to Roscommon in Castlebar was the main priority at Pairc Esler, but with 10 minutes to go, Down went in search of an equalising goal, but Chris Barrett, Keith Higgins and Colm Boyle all made crucial interventions.
"It was great to come up here and get the win. It was a tough game and we made a good few mistakes, but we did just enough to get through," he told RTÉ Sport.
"We rode our luck a good bit in the second half. I thought we did well in the first half, and once we got the goal we just stood off them a little bit and they caused us problems.
"The couple of games they had recently probably helped. They were flowing early. We struggled with their running at times. They got a good few goal chances in the second half, but thankfully our last ditch defending was strong and we got through.
"We're delighted to be in the draw for Monday."
In an early post-match assessment, what did Horan feel were the biggest concerns arising from the win?
"We gave the ball away at critical times, some of the decision making, the goal chances , some missed tackles up the field and letting runners through...but all very simple and fixable things."
Following the setback against Roscommon, Horan decided to change a third of his team with David Clarke, Colm Boyle and Andy Moran recalled.
The Mayo manager was asked whether the experience told in the end.
"It’s funny the way the game goes. Fionn McDonagh [who made his championship debut] got 60 minutes after his injury, Mike Murray made his debut, Kieran Treacy came on and Michael Plunkett came back on so by the end of the game we had a lot of young players.
"We did the same in the League; whoever is playing well from week-to-week gets a shot at it."
His counterpart Paddy Tally admitted that there were chances there for the taking for the home side.
"We'll probably look back with regret that we didn’t take more out of the game. We made three or four goal chances, we scored one and we missed a number of kickable scores and frees.
"The players though gave all they had and never gave upon it.
"Ultimately, against a team, like Mayo, if you are not clinical you will come up that bit short."