Saracens survived Glasgow's spirited second-half fightback to reach the semi-finals of the European Challenge Cup.

But the Guinness Premiership title challengers, who have now lost only one of their last 10 matches in domestic and European competitions, struggled to clinch a home semi-final clash against Bath.

They looked set for a comfortable victory after establishing a 13-0 lead after only 16 minutes but Glasgow ensured there was to be no easy passage through the quarter-finals.

Wingers Dan Scarbrough and Kameli Ratuvou scored the Saracens' tries with fly-half Glen Jackson kicking three penalties and two conversions, while Glasgow replied with full-back Rory Lamont's second-half try plus four penalties and a conversion from fly-half Dan Parks.

Jackson landed early penalties for Saracens, in the fifth and 11th minutes.

Five minutes later he intercepted a pass from opposite number Parks to hand Scarborough an easy try before adding the conversion.

But Sarries failed to press home their advantage and Scottish international Parks kept Glasgow in touch with three first-half penalties to a further one from Jackson.

The Saracens pack worked hard to stifle their opponents with skipper Simon Raiwalui and former Ireland hooker Shane Byrne getting through a lot of tackling.

Only a fine covering interception by Scarbrough denied the visitors a try with winger Thom Evans unmarked after centre Andrew Henderson split the Saracens defence.

Both sides were temporarily reduced to 14 players in the 47th minute of a sometimes niggly game when Glasgow number eight John Beattie and Richard Hill, England's World Cup-winning flanker, were sent to the sin-bin by French referee Christophe Berdos following a skirmish on the floor.

Another timely interception, this time by Jackson, frustrated Glasgow again as Lamont tried to find Evans before Saracens hit back almost immediately with their second try in the 52nd minute.

Centre Andy Farrell, making his return from the back injury which forced him to miss England's final two Six Nations matches, was stopped just short of the line after evading Graeme Morrison's tackle but he somehow managed to release the ball for Fijian winger Ratuvou to cross for his fourth try in his last three matches.

Saracens, leading 23-9, appeared briefly to be home and dry but Glasgow stubbornly refused to concede defeat, immediately hitting back with 10 points in the next six minutes.

Parks landed his fourth penalty and was also on target with the conversion after Lamont left Saracens standing as he burst through the middle for his 58th-minute try.

Saracens had to endure some hairy moments in defence but regrouped to hold out and make sure of their semi-final place.