Gopperth holds nerve as Tigers also advance
For the second consecutive season, Jimmy Gopperth will play in a Champions Cup semi-final after he held his nerve to slot a touchline conversion at the death.
Ulster-bound Charles Piutau crossed to leave Wasps trailing Exeter by a single point and Gopperth stepped up and bisected the posts to set up a semi-final date against Saracens.
Gopperth started for Leinster in their defeat to Toulon last year and Wasps' boss Dai Young hailed the Kiwi's nerve.
Former Ulster coach Mark McCall admitted that his Saracens side struggled against Northampton but they eventually ran out 29-20 winners.
JJ Hanrahan came on for Saints in the final five minutes and it was his error that allowed Chris Wyles in for a second try.
Leicester Tigers and Racing 92 will face off in the second semi-final which will pit two of the most promising Irish coaches (Geordan Murphy and Ronan O'Gara) against each other.
Elsewhere in the Challenge Cup, Conor O'Shea's Harlequins will host Bernard Jackman's Grenoble in the last four.