Saracens came from behind to secure top spot in the Premiership with a 23-14 win over Newcastle Falcons, while London Irish will finish bottom following defeat to Harlequins.
The identity of the four play-off semi-finalists had already been finalised after Leicester Tigers' win against Worcester Warriors on Friday, but Saracens cemented their position at top seeds with a game to spare.
A pair of tries from Marcus Watson inspired Newcastle to a 14-3 half-time lead at Allianz Park, but Sarries rallied in their bid to end the season at the summit
Jackson Wray repeated Watson's trick by crossing twice after the break, before Maro Itoje made sure of the victory for Saracens - for whom Jacques Burger was making his last appearance before retirement - by going over in the closing stages.
At the other end of the table, London Irish look set for Championship rugby next season after losing 32-25 to Harlequins.
Irish are now guaranteed to finish bottom and will be relegated if any team other than Bedford Blues, who did not meet the Premiership criteria, prevail in the second-tier play-offs.
Bedford were beaten 45-16 at home by Bristol in the first leg of their semi-final on Sunday.
Irish mounted a spirited fightback after trailing 22-15 at the break, moving 25-22 in front with the help of a David Paice touchdown.
But Harlequins stemmed the flow and Kyle Sinckler scored the try that left Irish hoping Bedford pull off a play-off success, with Newcastle surviving despite their defeat.
In the day's remaining match, Exeter Chiefs leapfrogged Wasps into second with 24-3 victory, moving two points clear of their opponents with a game remaining.