The reigning champions claimed a 31-27 victory after coming out on top in a dramatic 21-minute period either side of half time when six tries were scored, Saracens winger Michael Tagicakibau was sin-binned and flanker Justin Melck was sent off for what appeared to be eye-gouging.
Leicester hit back from 8-3 to take a 10-8 lead just before half time thanks to a penalty try, while further touch downs from Manu Tuilagi, Blaine Scully and Graham Kitchener ensured they took a bonus point.
Saracens' tries came from Ben Spencer (2), a penalty try and Jack Wilson, with Spencer's second four minutes from time earning his side a losing bonus point. They will play Harlequins, who beat Bath, in the other semi final at home.
Both sides were under-strength, especially Saracens who rested most of their top 30 players, with a Heineken Cup final and possibly the Premiership final on the horizon.
Lock Hayden Smith made his first start since rejoining Saracens, while England under-20 flanker Maro Itoje made his Premiership debut.
England and Lions flanker Tom Croft made his comeback for Leicester after suffering a knee injury which needed surgery in round one.
Leicester won the first half 10-8 but the small advantage came at a cost as the injuries started to mount with Owen Williams, David Mele, prop Boris Stankovich and lock Geoff Parling all picking up knocks.
Stankovich lasted less than a minute before he trooped off, to be replaced by Marcos Ayerza, after suffering an injury at a ruck.
Things got worse for Leicester a minute later when a lively Saracens team took the lead after some bright play resulted in scrum-half Ben Spencer making a break through the front of a ruck. Although he was held short of the line he reached and put the ball down over the line.
Former England fly-half Charlie Hodgson missed the conversion on an afternoon when the strong wind made it difficult for the kickers, and three minutes later Williams pulled three points back with a penalty from in front of the posts.
Saracens came close to scoring a second in the eighth minute after Hodgson beat Thomas Waldrom on halfway and made a fabulous break. Although the Tigers managed to prevent a try they conceded a penalty, which Hodgson slotted.
Williams missed a long range penalty before he, and then Parling, suffered injuries and were replaced by Dan Bowden and Kitchener.
The loss of Williams meant Toby Flood moved to fly-half, with Bowden taking over at centre, and with two minutes of the half left Bowden made a fine break which almost led to a try after great work by Niall Morris, Ayerza and Steve Mafi.
Saracens' defence, however, held firm and Mele went off, to be replaced by Sam Harrison, after a tackle by Smith near the line. Mele returned for the second half.
Leicester, however, marched Saracens back from the resulting scrum and the referee awarded a penalty try, with Flood adding the extras to give the Tigers a 10-8 half-time lead.
Within four minutes of the restart that lead had become 17-8 and Saracens were reduced to 13 men after winger Tagicakibau was sin-binned for a tip tackle on Ayerza and flanker Melck sent off for what appeared to be gouging.
A minute after the yellow card, Leicester's forwards rumbled towards the line and Flood put Tuilagi over under the posts.
Four minutes later Leicester got their third try in nine minutes, Morris making a break before passing inside for fellow wing Scully to score, Flood adding the conversion.
Saracens hit back in the 54th minute, the referee awarding them a penalty try after Leicester had collapsed a terrific rolling maul. Ben Spencer converted to make it 24-15.
Four minutes later, Kitchener scored at the other end, Flood converting, and Croft immediately replaced Mafi.
Croft had hardly got on the field when Saracens winger Wilson scored his side's third try. In 20 frantic minutes both sides had scored six tries and Saracens had been shown a yellow and a red card.
With four minutes left Spencer intercepted a pass from Thomas Waldrom and ran 70 yards to score in the right corner before converting, but the Tigers were able to close out the victory.
- Sports & Recreation