Bath could hardly have wished for a more encouraging May day beside the River Avon. A comfortable win over the Premiership leaders was almost the lesser bonus compared with the unexpected prize of a home semi-final. Sale have done them a mighty favour which may not be repaid when the Sharks head to Somerset in the last four a week on Saturday.

Admittedly this was largely a Northampton second string but Bath are precisely the kind of team who could finish the season at a proper gallop. Powerful up front and hard to contain behind, Johann van Graan’s side are now 80 minutes away from a first Premiership final for nine years and, historically, home semi-final advantage has proved a significant advantage.

Related: Risk v reward: equation that turned Bath into Premiership dark horses

Stir in a lovely early summer’s afternoon and it added up to a near-perfect day for Bath’s supporters, who have waited an awfully long time for the fates to turn in their favour. While they did not need to be at their absolute best, a try count of six to two told the story of a one-sided contest which underlined the squad depth at their disposal.

It has also been a remarkable climb from the foot of the table two years ago to their current elevated position, with Van Graan highlighting the input of his half-backs Finn Russell and Ben Spencer. Russell had another tactically influential game and his coach remains a massive fan of his fit-again fly-half. “The game is about big players in big positions,” said Van Graan. “What Finn went through in the last few weeks to get back in this position was phenomenal. That was a significant injury...he worked day and night with our medical team. I can’t speak highly enough of him.”

If the biggest roar of the game was reserved for Spencer’s 54th-minute interception score which secured the bonus point that guaranteed Bath’s playoff place, the consistent impact of the home set piece and the ruthless way in which they cut loose in the final quarter also bodes well for the knockout stages. They could even afford to wrap Russell in cotton wool long before the end with the job long completed.

It was a far cry from Northampton’s 90-0 thrashing of Gloucester last week, as it was destined to be from the moment the Saints named a side containing 13 changes. They will clearly be a stiffer proposition in the semis and deserved to finish top of the regular season table but here was another reminder that the playoffs are as much about which side finishes the strongest.

There was certainly no doubting the intent of the Bath pack from the moment they rumbled over for a pushover try finished by Josh Bayliss. Inside a quarter of an hour they had a second, a beautiful line-straightening assist by Russell sending an accelerating Will Muir clear.

• Download the Guardian app from the iOS App Store on iPhone or the Google Play store on Android by searching for 'The Guardian'.

• If you already have the Guardian app, make sure you’re on the most recent version.

• In the Guardian app, tap the Menu button at the bottom right, then go to Settings (the gear icon), then Notifications.

• Turn on sport notifications.

Saints did dig in for a while and were rewarded with a try just before the interval for James Ramm, making the most of the Bath full-back Matt Gallagher having been sin-binned two minutes previously. It never seemed likely to be a major turning point and so it proved. Another surge delivered a third home score, finished by hooker Tom Dunn, before Spencer’s 55-metre breakaway sealed the four-try bonus.

The only surprise was that Bath did not score again after replacement Alfie Barbeary and a charging Muir added further tries in the final quarter but it mattered little. On days like this, with a full ground basking in the sunshine at the Premiership’s most scenic venue, it seems strange that club rugby’s popularity is not more widespread. And equally hard to believe Bath will not be a real handful in the semi-finals.

Saints’ director of rugby Phil Dowson was underwhelmed by his side’s performance. “It’s frustrating and a bit disappointing,” he said. “We felt we had enough quality in the group to put up more of a challenge than that. We just didn’t come out of the blocks in the first 20 minutes. And when you’re 17-5 down at half-time and then concede immediately it’s a long way back.”