London Irish edged a thrilling Guinness Premiership encounter against Saracens on Saturday at the Madejski Stadium, hanging on for a 27-24 victory.
Despite the return to fitness of Glen Jackson, Saracens slumped to a fifth loss in their last seven games as the fly-half missed a penalty in the final minute.
Saracens have now scored just eight tries in their last six games and with Exiles' Peter Hewat in fine form to notch up 17 points, Ben Skirving and Kameli Ratuvou touchdowns were never going to be enough for the visitors.
After an opening five minutes dominated by Saracens, the mercurial Jackson kicked the first points in the seventh minute with a 30-metre penalty in front of the posts.
Irish, who controversially slumped against Saracens back in November, were in front by 14 minutes as two penalties from Hewat handed the Exiles the advantage.
Saracens were reduced to 14 men in the 26th minute when lock Kris Chesney was sin-binned for diving over at the breakdown.
Hewat kicked another penalty to take Irish six points clear only to be pegged back after Jackson slotted his second penalty after thirty minutes.
Irish doubled the lead three minutes later when Hewat kicked a penalty from 20 metres after Saracens second-rower Hugh Vyvyan was caught with his hands in the ruck.
But a Skirving try two minutes before the break was converted by Jackson, meaning Sarries took a one-point lead into the interval against the run of play.
Jackson extended his side's lead and his tally with another three points in the 49th minute after the New Zealander had missed a kick minutes earlier.
London Irish regained the lead in the 54th minute after winger Topsy Ojo broke through the Sarries back line. The former England U21 international slipped the ball to Tagicakibau and the 24-year-old went over for his first of the season.
Another breakaway try four minutes later from Tiesi kept the Exiles in front as they mounted yet more misery on their guests.
Jackson reduced the deficit to five points when he converted another penalty as Sarries started a mini-revival.
But the home side fought back and Hewat extended Irish's lead in an economical kicking display taking his personal tally to 17 points.
Ratuvou went over for Sarries in the 74th minute but it proved too little too late for the out-of-form visitors as Jackson missed his kick late on.
For London Irish:
Tries: Tagicakibau, Tiesi
Pens: Hewat 5
Tries: Skirving, Ratuvou
Pens: Jackson 4
Yellow Card: Chesney (Saracens - 26th minute)
London Irish: 15 Peter Hewat, 14 Topsy Ojo, 13 Delon Armitage, 12 Seilala Mapusua, 11 Sailosi Tagicakibau, 10 Mike Catt, 9 Paul Hodgson,8 Richard Thorpe,7 Steffon Armitage, 6 Kieran Roche, 5 Bob Casey (c), 4 Nick Kennedy, 3 Faan Rautenbach, 2 David Paice, 1 Tonga Lea'aetoa,
Replacements: 16 Dan Murphy, 17 Stuart Mackie, 18 Richard Skuse, 19 James Hudson, 20 Declan Danaher, 21 Warren Fury, 22 Gonzalo Tiesi
Saracens: 15 Dan Scarborough, 14 Richard Haughton, 13 Francisco Leonelli, 12 Adam Powell 11 Rodd Penney, 10 Glen Jackson, 9 Neil De Kock (c), 8 Ben Skirving, 7 David Seymour, 6 Paul Gustard, 5 Hugh Vyvyan, 4 Chris Jack, 3 Cobus Visagie, 2 Fabio Ongaro, 1 Nick Lloyd.
Replacements: 16 Andy Kyriacou, 17 Cencus Johnston, 18 Tom Ryder, 19 Kris Chesney, 20 Alan Dickens, 21 Brent Russell, 22 Kameli Ratuvou.
Referee: Dave Pearson
Touch judges: Andrew Pearce, Roger Baileff
Television match official: Bob Ockenden