Harlequins wrapped up fourth spot in the Premiership to secure the final playoff spot and a semi-final against Saracens by beating Bath.
A try from Mike Brown, as well as four Nick Evans' penalties, were just enough to settle an even game at 19-16.
Bath held fourth spot at the start of the day, but a solid Quins performance was enough to see them through.
The visitors will feel this season was an opportunity wasted, as they fell short despite such a strong start to the season.
Harlequins reward for the win is the unenviable task of taking on favourites Saracens at Allianz Park, in what will be a real test of Quins' desire and talent.
The nerves felt by both sides were plain to see early on in a frantic, error strewn opening ten minutes. It was the home side who made the breakthrough after a fractious start.
The try will have pleased England head coach Stuart Lancaster, as Danny Care threw a huge wide pass, which gave Brown an easy run in to the corner. The pair, who will likely be key players in the tour of New Zealand, sent the Stoop wild, with Evans adding the extras.
Bath rarely threatened, but with players like George Ford, they don't need to threaten to score points.
The fly-half picked the ball up 40 metres out, and slalomed through what felt like an endless sea of tackles to dance over for one of the tries of the season.
Conor O'shea's men responded immediately, but were stung by TMO David Grashoff, who judged that Care had thrown a forward pass when setting up Nick Easter for a try under the posts. Evans' penalty gave the hosts a 10-7 half time lead.
Whilst the away side had struggled at times in the first half, they came out after the break with a renewed spirit, as Nick Abendandon came agonisingly close to giving Bath the lead.
Ford's penalty did at least level up the scores. One thing Mike Ford didn't need was his side to go down to 14 men, but that was the case when Matt Banahan was sent to the bin.
They did pay for that yellow card, though it could have been a lot worse. Quins probed but just couldn't find the elusive try, before eventually settling for three points, courtesy of Evans' boot.
It was a game of tight margins, with another Evans penalty giving Conor O'Shea's men a six-point lead.
As the game approached the last 15 minutes, Bath kept themselves in touch with a Ford penalty.
The two fly halves traded penalties again to leave the game on a knife edge as the clock ticked down. Quins then held firm to deny Bath a win, with a Ford drop goal charged down with the clock past 80 minutes.
Their season isn't over though, as they take on Northampton in the Challenge Cup final in Cardiff.
Pens: Evans 4
Pens: Ford 3
Yellow Card: Banahan
Harlequins:15 Mike Brown, 14 Tom Williams, 13 Tim Molenaar, 12 Jordan Turner-Hall, 11 Ugo Monye, 10 Nick Evans, 9 Danny Care, 8 Nick Easter, 7 Chris Robshaw (c), 6 Maurie Fa'asavalu, 5 George Robson, 4 Charlie Matthews, 3 Kyle Sinckler, 2 Dave Ward, 1 Joe Marler.
Replacements: 16 Rob Buchanan, 17 Mark Lambert, 18 Will Collier, 19 Nick Kennedy, 20 Tom Guest, 21 Karl Dickson, 22 Ben Botica, 23 Sam Smith
Bath: 15 Nick Abendanon, 14 Anthony Watson, 13 Jonathan Joseph, 12 Ollie Devoto, 11 Matt Banahan, 10 George Ford, 9 Micky Young, 8 Leroy Houston, 7 Guy Mercer, 6 Carl Fearns, 5 Dave Attwood, 4 Stuart Hooper (c), 3 David Wilson, 2 Eusebio Guinazu, 1 Paul James.
Replacements: 16 Tom Dunn, 17 Anthony Perenise, 18 Juan Pablo Orlandi, 19 Dominic Day, 20 Alafoti Fa'osiliva, 21 Peter Stringer, 22 Gavin Henson, 23 Semesa Rokoduguni.
Referee: Wayne Barnes
Assistant Referees: Paul Dix, Nigel Carrick
TMO: David Grashoff