Kelly Brown went over for Glasgow's first try

Sean Lineen's men were desperate to claim a precious bonus point to set up a dramatic Pool Four decider with Saracens at Firhill next Friday.

The Warriors grabbed the win - but could not rattle up the necessary four-try tally.

Both sides made a jittery and disjointed start with the Italian hosts getting marginally the better of the initial sparring session.

They were awarded a penalty in the seventh minute when the Glasgow cover defence crept offside, but former Warriors hero Calvin Howarth sent his effort past the post.

The relieved Scots strung together a series of slick moves, but without really looking like inflicting immediate damage.

Play continued to be messy until the mid-point of the half, when the contest suddenly burst into life.

Glasgow surged ahead with a superbly-worked try by breakaway forward Kelly Brown - only to be pegged back almost instantly.

Colin Gregor made the telling thrust into the Viadana danger zone and after he was hauled down, the alert Dan Parks launched a beautifully-weighted chip to the right flank.

Brown was lurking all on his own and after bouncing off the challenge of Kaine Robertson, he was left with a cruise to the line.

Parks followed up with a pinpoint conversion - but the joy of the Warriors lasted a matter of seconds.

From the restart by Howarth, Glasgow skipper Ally Kellock palmed back the ball in an uncontrolled manner.

And from the loose ball, the home brigade created the sequence which led to South African number eight Jaco Erasmus ploughing over.

Howarth made amends for his penalty bungle by slotting the goal from an awkward angle to tie up the scores.

And the Warriors suffered a further major setback four minutes before the interval - with Erasmus again emerging as the hitman.

Howarth's cross-kick was gathered by Colin Shaw, but he slipped on the greasy surface as he prepared to hoof the ball clear.

He was engulfed by several Viadana markers and was forced to give away a penalty for holding on to the ball too long.

Erasmus caught the Glasgow defence on the hop with a quick tapped kick before bullocking his way to the target.

And the score was awarded by French referee Jerome Garces on the say-so of his video assistant.

Howarth was off-target with the conversion - and there was still enough time for Parks to steady the Warriors' nerves with a penalty.

Both outfits made a spate of changes at the restart in a bid to seize the initiative and it was Glasgow who were next on the scoresheet with another penalty by Parks.

They were still toiling to find penetration in attack, however, and it was not until the start of the last quarter that they imposed their authority through a touchdown from Argentinian full-back Bernie Stortoni after another kick from Parks.

His effort set up a tension-packed finale.

Substitute Corrado Pilat - on for Howarth - narrowed the leeway to just three with a penalty five minutes from the end.

"It was not a great game," admitted Glasgow coach Sean Lineen. "They made it hard for us, we made it hard for us, and the referee made it hard for us.

"Viadana were struggling in the contact phase but a weak referee let anything go. They were offside all the time, but we did not deal with that situation."

Sean added: "I want to focus on the fact that we won – the first away success for Glasgow in 28 Heineken Cup games. There was no bonus point, but it had been lashing all day and the ground was very soft.

"They way we have been playing, I'll take the win. We only scored two tries, but we also created both their scores."