Saracens produced an amazing second-half comeback to avoid a major Heineken Cup shock against Italian minnows Viadana despite trailing by 23 points at the interval.

Sarries scored 31 unanswered points in the second half to get out of jail after looking dead and buried when the home side ran in four tries in the opening 40 minutes.

Glen Jackson led the fightback with a personal haul of 19 points and tries for David Seymour, Richard Haughton and a penalty try left the Saracens players and 200 travelling supporters breathing a huge sigh of relief.

The home side were clearly taking this game more seriously, making 10 changes to their starting line-up from last week's 71-7 defeat in Watford including a return for Italian internationals Kaine Robertson and Josh Sole.

The home side lit up the stadium after some morning snow with their inventive and intensive rugby - taking the lead after just three minutes when Jaco Erasmus crossed in the corner.

It got worse for Saracens a minute later when, from the restart, they lost hooker Matt Cairns with an arm injury to be replaced by Fabio Ongaro.

Despite the early setback, the visitors did show some early signs of pressure with their forward pack looking the stronger of the two. That pressure told to create an opening for Ben Skirving, but as he reached out to touch down, pressure from the home side knocked the ball clear.

It got worse when Erasmus went over for his second of the afternoon after picking off a floated pass inside the Saracens 22 to score under the posts. Calvin Howarth converted.

Glen Jackson reduced the arrears with a penalty midway through the half but Saracens were being drawn into the frenetic style of play favoured by the home side.

That cost them after half an hour when a turnover on halfway - one of 10 in the first half given away by Saracens - saw prop Ignacio Rouyet burst through and set up full-back Steve Bortolussi to score under the posts. Howarth added the extras.

And with time running out, Robertson took advantage of a break from Samuele Pace to cross in the corner. With Howarth again adding the extras, it left Saracens needing to turn around a 23-point deficit in the second half.

Jackson added another three points straight from the restart before the forwards earned a try after forcing the home side into three penalties from a five-metre scrum. Referee Peter Fitzgibbon went under the posts for a penalty try, converted by Jackson. The fly-half added another three points soon afterwards to take Saracens within 10 points.

And when home flanker Sole entered the sin bin, Jackson took full advantage to take the game to within a converted try.

That came on the hour mark when Brent Russell and Haughton swapped passes on halfway allowing the latter to go on a mazy run and he released Seymour to cross in the corner. Jackson converted to level the scores.

After more sustained pressure in the Viadana 22, the home side were penalised again for not rolling away and Jackson remained calm to kick his side into the lead for the first time in the match.

And the comeback was complete with the final play of the game when Haughton backed himself to go around two forwards on the wing to cross the line.