In steadily worsening conditions Ryan Lamb's penalty four minutes from time had put Saints in a position to get at least one league point and enough time to have a go at what would have been a winning try. But just as they had in the LV= Cup meeting a few weeks before, Harlequins kept on playing until the final whistle, and with the last play of the game Evans broke home hearts.
One of the great things about the Franklin's Gardens pitch is its ability to hold up despite heavy rain.
Nearly an inch fell on Northampton Friday night into Saturday morning, but last summer's investment into the pitch drainage system paid dividends by kick off and not only was there a dearth of puddles but both teams were able to start on as good a playing surface as anywhere in the country this weekend.
The rain had gone, too, and while it had returned before half-time Harlequins showed their intent by putting the ball through the hands early to put Saints under pressure.
The aforementioned LV= Cup clash had seen 61 points and six tries shared between the Saints and Quins, and had the conditions held up then something similar could have been on the cards in the Aviva Premiership Rugby re-match.
Quins stretched Saints with their dummy runners from deep and pacey attack, but it was their forward who brought the first points with a powerful scrum that handed Evans the opportunity to kick at goal.
The home eight got some semblance of revenge straight away, setting up a superb maul which rolled the best part of 20 metres upfield. However Quins eventually managed to disrupt and when Tom May was outnumbered in a midfield charge the ball was turned over.
And while there was a let-off when Matt Hopper dropped a pass cutting an angle into the home 22 Saints remained positive, Stephen Myler chipping into space and Ken Pisi taking on Maurie Fa'asavalu on the outside.
The hosts also had a great chance just before the half-hour, when Samu Manoa - who had an excellent start to the match - charged down and recovered an Evans kick to power into the visitors' red zone. There were a few shirts in support, but with trailing Quins scrambling back there was no opportunity to get the scoring pass away.
However Manoa did set up the play for Saints' first points, catching a Myler 22-metre restart and giving Lee Dickson the perfect platform to send a box kick from which Tom Wood and GJ Van Velze won a penalty to give their fly half a shot at the uprights.
This tied things up, and Saints kept on coming, and their next attack did not get the reward it deserved. Myler sent a free kick to the skies, with the excellent chase winning the ball back. Tom May took play left, and when George Pisi tapped on Mike Haywood's pass Ben Foden showed his pace, evasiveness and power to take him over the whitewash.
It would have been an excellent try that would surely have given Saints a huge psychological boost, especially with the weather starting to deteriorate. But referee Wayne Barnes had other ideas, having called a forward pass rather than go to the TMO.
Harlequins had escaped, and as the rain started to come down in increasing strength the contest became more of a kicking duel. Myler's next shot at the sticks stayed agonizingly to the right, but while Evans re-took the lead it was the home fly half who caught the eye with a Sevens-style flick between his legs to keep play alive.
There was an overlap created, spoiled only by a Courtney Lawes fumble, and when a touchline penalty was kicked to the corner another chance ended when George Robson took the ball against the throw.
Saints had put themselves in the positions in the first half but had not been able to finish things off. But when Myler tied things up again four minutes from the hour they were in a position from which to kick on and try to take control.
James Johnston had spoiled an otherwise impressive afternoon with a yellow card following a searing combination between Jamie Elliott and Foden up the left wing, and with Myler kicking to the corner before the Samoan had even left the field the intent was obvious.
However instead it was Harlequins who grabbed the initiative, Evans landing two penalties to give the visitors a six-point margin. But while Saints were having to chase the game the conditions were now such that putting the ball through the hands was risky at best. So the ball went to the air; not a bad tactic considering that the chasers were still heading upfield with purpose and the wind and rain were making catching very difficult.
But Saints were finding that Mike Brown was becoming increasingly imperious under the high ball in his man of the match performance, and with this foundation at the back Harlequins were not just able to hold the hosts at arm's length but also increase their lead to 15-6.
With nine minutes to play the half-backs were swapped to immediate effect. Martin Roberts and Ryan Lamb hit the line at pace, and the first backs move of any note from either team forced Tom Williams to concede a lineout five metres out. Williams's petulance then saw a penalty awarded, and Lamb shrugged off the pressure to put his team back into striking range on the scoreboard.
There was enough time to mount one last attack in search of what would have been the winning try, but a fumble at a lineout handed Harlequins possession inside the home 22, and when the penalty came up stepped Evans for the final, cruel say.
4mins QUINS Pen Evans 0-3
15mins QUINS Miss pen Evans
17mins SAINTS Pen Myler 3-3
23mins SAINTS Miss pen Myler
37mins QUINS Pen Evans 3-6
HALF-TIME SAINTS 3 HARLEQUINS 6
47mins QUINS Miss pen Evans
54mins QUINS Yellow card Johnston
56mins SAINTS Pen Myler 6-6
62mins QUINS Pen Evans 6-9
66mins QUINS Pen Evans 6-12
71mins QUINS Pen Evans 6-15
75mins SAINTS Pen Lamb 9-15
80mins QUINS Pen Evans 9-18
FULL-TIME SAINTS 9 QUINS 18