Because with six minutes to go a rain-soaked at cinch Stadium at Franklin’s Gardens on Saturday afternoon, it looked like Saints’ 100 per cent start to the season would be washed away.
London Irish had swept back from 17-0 down to lead 21-20 and, in truth, Saints seemed to have run out of solutions.
Nothing would stick as lineouts were lost and passed were spilled. It was infuriating for the hosts.
But when Tuisue put his head into the face of Alex Waller, referee Tom Foley had a decision to make.
It was at the very minimum a penalty, and that was what arrived, allowing Biggar to give Saints a priceless lead on a day when home points became increasingly hard to come by.
Irish still had time to respond and, with the clock in the red, Saints showed great desire to charge down a Paddy Jackson drop goal attempt.
The ball went wide and that seemed to be that.
There was still for another TMO intervention but Foley stayed strong and refused to give a penalty against Courtney Lawes.
It would have been an obscene decision if Lawes had been penalised for a no-arms tackle, in which he clearly used both arms.
And eventually the right decision was made, with Foley bringing an end to the game there and then.
Saints know they that if they were playing a game of Monopoly, they would have used up their get-out-of-jail free card.
Because Irish really didn’t deserve to lose this game and Saints didn’t really deserve to win it.
Yes, they played well during the formative stages of the game, racing into a 17-0 lead that they only looked likely to build on at that point.
But from then on, the Saints were sinners, losing two men to the sin bin and tiring out Foley’s arm as he continually raised it to give penalties to Irish - 16 in total.
It could have been a tale of woe for Saints.
Another post-Exeter hangover, as in February when Saints won at Sandy Park only to return home eight days later and lose narrowly to Bath.
But in the end, it was the opposite.
Rather than talking about how this is the old Saints, being stung by a sucker punch, we’re talking about how good teams win games like this.
As boss Chris Boyd said after the game, he doesn’t consider Saints to be one of those good teams yet.
But they are certainly building something.
They have now won three from three at the start of this season.
And though none of the performances have been comprehensive or convincing, Saints have shown they have different ways to win with their backs against the wall.
Again in Boyd’s words, they were finding new ways to lose during their barren spell last year, racking up home defeat after home defeat.
But they have spun that situation around so far this season.
And long may it last.
How they rated…
Not an easy day to be a full-back and there were some tough moments, but his assist for Matt Proctor was a thing of beauty in slippery conditions... 6.5
Played his part at the breakdown, showing his all-round ability, but didn't have many attacking opportunities... 6
Now looks right at home in the Saints back-line and has scored two tries in as many games, while also showing his worth defensively... 7.5
Another strong showing from the centre, who was in the thick of the action, showing his physicality in attack and defence... 7
Etched his name on the scoresheet with a trademark finish, but had a couple of tough moments defensively... 6.5
DAN BIGGAR - CHRON STAR MAN
Pulled the strings for Saints in difficult conditions, looking typically assured throughout and battling on after taking some heavy hits... 7.5
Really set the tempo for Saints early on, fizzing the ball about and making inroads, but life got tougher for the scrum-half and he missed a few tackles... 6.5
A steady showing from the prop, who earned the right to start and who didn't let his team down... 6.5
A strong and fired-up display from the hooker, who could be seen rallying the troops and who kept the attacking set piece largely secure... 7
The prop was perhaps harshly sin-binned as he tried to help Saiints stem the tide against an Irish team who put plenty of pressure on... 5.5
Got stuck in for his team and was keen to take the fight to Irish, but he did find himself on the wrong side of the referee on a couple of occasions, as most of the home team did... 6
Worked hard during his time on the field but it was limited due to a yellow card he received with Irish on top... 5.5
Made one crucial turnover for his team as he just kept going and going once again, putting in another big shift... 7
Got through plenty of tackles before being withdrawn during the second half, and there was no shortage of effort once again... 6.5
Was a key man during the early stages of the game, putting Irish under real pressure with his power and running ability... 7
Replacements (who played more than 20 minutes)
ALEX WALLER (for Auterac 50)
Conceded a couple of penalties but played his part in the win as he managed to rattle Albert Tuisue to earn the shot at goal that eventually proved decisive... 6.5
COURTNEY LAWES (for Ludlam 55)
Was welcomed with a big cheer as he entered the field and he enjoyed a strong cameo, winning the ball back and helping to see his side over the line... 7
EHREN PAINTER (for Hill 57)
Didn't get involved too much but didn't do much wrong either as Saints eventually got the job done... 6
TEIMANA HARRISON (for Augustus 57)
Loves a scrap and this is exactly what this was as he flew around the field, making tackles and carries for his team... 7