LONDON (Reuters) - Saracens produced a terrific all-round performance to overwhelm the heavily favoured Ospreys 19-10 on Sunday and advance to the Heineken Cup semi-finals.

Both sides were appearing in the last eight for the first time but Saracens were in control for most of the game against a visiting team who thrashed them 30-3 in the EDF Energy Cup semi-finals two weeks ago and contained the bulk of the Wales team who won the Six Nations grand slam last month.

Saracens led 6-3 at halftime after two Glen Jackson penalties, though they should have been further ahead as the Ospreys failed to spark.

The game turned decisively in Saracens' direction two minutes after the restart when Argentine replacement Francisco Leonelli ran 60 metres to score the opening try.

Jackson converted from the touchline and then added his third penalty to raise the volume at Watford FC's Vicarage Road, sold out for a Saracens game for the first time.

The Ospreys finally got going in the last quarter and replacement Paul James ended several minutes of forward pressure to score a converted try to cut the lead to six with six minutes remaining.

Saracens though, kept their heads and set up Jackson for a sharply-taken drop goal to take it to 19-10 which proved enough.

In the semi-finals on the weekend of April 26/27, Saracens will play Munster at Coventry's Rioch Arena after the Irish province overwhelmed Gloucester 16-3 away on Saturday.

The second semi will be at Twickenham where London Irish, in the last four for the first time after beating Perpignon 20-9 on Saturday, will play Toulouse or Cardiff Blues, who meet in the last quarter-final later on Sunday.

(Reporting by Mitch Phillips; Editing by Sonia Oxley)