These are the kind of games that can catch Ulster out, and at half-time at Kingspan Stadium the crowd were starting to feel it.
It was exactly the kind of night their head coach Dan McFarland had warned us about back in October; Ulster were favourites, coming into the game off a high, and their opponents looked bang out of form.
But as the sides jogged into the changing rooms on 40 minutes there were just seven points between them despite Ulster outscoring the away side by three tries to one, Rob Herring and Ethan McIlroy crossing either side of a penalty try.
They'd lost Stuart McCloskey to a 17th minute hamstring injury, and their discipline was allowing Northampton's out-half George Furbank keep his side in within touching distance off the tee.
The half-time break was needed, and while Ulster looked less explosive in the second 40, they were crucially more composed at times, even after losing Iain Henderson to injury in the early stages.
John Cooney managed the lead back to double digits with a penalty before Craig Gilroy brought up the bonus point.
They saw out the victory to make it two wins from two in the Heineken Champions Cup, but not without some discomfort as a pair of Northampton tries saw them pick up a losing bonus point and provide a nervy final minute.
After last week's dismal defeat to Racing 92, Northampton brought Courtney Lawes and Ahsee Tuala into their side among six changes, but once again seemed to start the game five minutes later than their opponents, letting Herring in for a try inside 120 seconds.
With controlled possession on the edge of the 22 it was the in-form Hume who found the gap, stepping inside a defender, before offloading to McCloskey, who recycled the ball. Billy Burns dropped a delicate, delayed pass to Herring, whose infield line brought him under the posts, which Cooney easily converted.
Despite such a passive start, Northampton out-half Furbank picked off three points shortly after, as Iain Henderson was penalised for not rolling away.
While Ulster were comfortably the better side, the presence of Lawes in the Saints line-up was putting some fire into their fight, and the Test Lion made his presence known with a crunching hit on Henderson.
Northampton were struggling to contain the home side though, who gave themselves the platform for their second try with a wonderful 50:22.
Playing with penalty advantage, Cooney sniped right and swung a pass to Gilroy on the wing, which Saints scrum-half Alex Mitchell grabbed at.
Mitchell could - and arguably should - have intercepted the pass but knocked it on, and after a check with the TMO, his one-handed attempt to catch it cost him a yellow card and a penalty try against his team, a second Ulster try inside 12 minutes.
With the scores 12-3 and a man down for the next 10 minutes, Furbank wisely popped over a second penalty when Marcus Rea infringed shortly after the restart, but Ulster's lead was extended on the 20th minute in spectacular fashion.
Once again, Hume was the architect. The centre was inside his own half when he dribbled a grubber kick behind the Saints frontline, and McIlroy timed his run beautifully through the middle as he collected and threw a dummy.
Ollie Sleightholme recovered to catch McIlroy a couple of metres short, but the winger did brilliantly to reach over his shoulder and touch down.
Cooney's conversion rattled the post, and some poor Ulster discipline allowed Northampton back into the game, as penalties for obstruction and sealing off allowed Furbank kick a further six points, bringing the scores back to 19-12 by the time the half-time whistle sounded to a frustrated Ravenhill.
They started the second half in determined fashion, Rea winning a penalty on the edge of the 22 following some good, sustained pressure. Cooney took the safe option and pointed for the posts, his kick making the scoreline look healthier at 22-12.
Having lost McCloskey to a hamstring injury in the first half, there was the unwelcome sight of Henderson limping off on 47 minutes, the skipper having also missed the last four weeks due to a hamstring issue.
McFarland's side had the bonus point in sight, and the longer they went without getting one, the edgier the Belfast crowd were getting.
Duane Vermeulen drove into the 22 before a knock on from the support. Shortly after Andrew Warwick broke the line and offloaded to Herring, only for Ulster to go off their feet a couple of phases later.
It was frustrating at times, but their overall control of the game left the feeling that the fourth try wasn't far away, and it arrived on 57 minutes.
It started with Ulster disrupting a Northampton lineout five metres out, before they doubled up and won a penalty off the scrum. Burns kicked to the corner, before an early Saints drive on Alan O'Connor gave the attacking team a penalty advantage.
Playing with house money, Burns dropped a crossfield kick to the right wing, and it slipped through the hands of Tuala for Gilroy to catch and score his 68th Ulster try on his 201st appearance.
The first half had been marked by Ulster switching off right after they scored, and it happened again as they allowed Northampton in for their first try on the hour mark, Mitchell sliding off a poor Gilroy tackle attempt. With Furbank missing the conversion, the Ulster lead was back down to 10 points at 27-17.
Having folded against Racing seven days ago, Northampton to their credit kept coming back at Ulster in the hope of at least a losing point, with Lawes making a nuisance at the lineout.
And they deservedly crossed for a second try as the clock hit 78 minutes, Courtnall Skosan finishing off an excellent counter attack in the corner.
Furbank's conversion drifted wide to leave five between the sides and 60 seconds on the clock, but there was no dramatic ending as an Ulster penalty shortly after the restart saw Burns boot the ball into the stands and bring up the full-time whistle.
Ulster: Mike Lowry; Craig Gilroy, James Hume, Stuart McCloskey, Ethan McIlroy; Billy Burns, John Cooney; Andrew Warwick, Rob Herring, Marty Moore; Alan O'Connor, Iain Henderson (capt); Marcus Rea, Nick Timoney, Duane Vermeulen.
Replacements: John Andrew, Jack McGrath, Tom O'Toole, Kieran Treadwell, Sam Carter, Nathan Doak, Stewart Moore, Greg Jones.
Northampton: Ahsee Tuala; Ollie Sleightholme, Matt Proctor, Fraser Dingwall, Courtnall Skosan; George Furbank, Alex Mitchell; Alex Waller, Mikey Haywood, Ehren Painter; David Ribbans, Api Ratuniyarawa; Courtney Lawes, Lewis Ludlam (capt), Tom Wood.
Replacements: James Fish, Emmanuel Iyogun, Conor Carey, Alex Coles, Juarno Augustus, Tom James, James Grayson, Rory Hutchinson.
Referee: Andrea Piardi (ITA)
