McDonnell blasted home in injury-time as the Orchard men won out despite early injuries to Ciaran McKeever, Charlie Vernon and Gareth Swift.

Louth took a 0-07 to 0-05 lead into the break with Darren Clarke (0-03) and Christy Grimes (0-02) impressing.

Armagh fought back to level at 0-09 apiece, Paddy Keenan and Mark Stanfield replied for Louth before McDonnell provided the sucker punch.

Malachy Mackin got a straight red card for Armagh while the visitors had Colin Goss dismissed.

There was tension in this game even before John Bannon threw the ball in.

Both teams went to warm up at the same end and with nobody moving, there were a couple of confrontations before the Longford referee and his umpires quickly stepped in.

The razor-sharp Clarke cracked over the opening two points for Louth - frees in the second and fourth minutes - but Eamon McEneaney's charges were dealt a blow when their skipper Peter McGinnity was stretchered off, with Alan Page replacing him.

The Armagh attack worked Paul Keenan in for their first point, in the 10th minute, before Louth, winners over Down last week, pulled clear into a 0-05 to 0-02 lead with Grimes and Clarke raising white flags.

The difference was narrowed to two points at the break as Peadar Toal, McDonnell and Malachy Mackin reduced the arrears for the 2005 league champions, who did well to bounce back after losing both of their starting midfielders - Swift and Vernon - through injury.

In front of a crowd of more than 7,000, the hosts began the second half well but had little sway on the scoreboard as McDonnell, who was guilty of a number of bad wides, hit over their only point for 15 minutes.

He added a second free, replying to a Paddy Keenan point, before Clarke edged Louth into a 0-9 to 0-7 lead.

Armagh dug deep to square up the game, but when last year's Division Two champions, playing a very effective short-passing game, landed two late points - through Keenan (66) and Stanfield (70) - Armagh's number seemed up.

Ironically, Stanfield, who is a club-mate of McDonnell's at Killeavy, could have gone for a goal when put clean through but opted for the point and he paid a heavy price as, in the last play of the game, a high ball in from Paul McGrane wormed its way through to McDonnell and he clinically made no mistake.