Sleightholme scores twice as Saints secure thrilling win against Harlequins
Sleightholme scored his side's first and last tries of the night as they eventually opened up a 10-point gap late on.
But Quins kept coming and Nathan Jibulu's last-gasp try got nerves jangling at cinch Stadium at Franklin's Gardens.
However, Saints saw it out with the clock in the red, allowing them to secure a 36-33 victory on a night when they lost both Lewis Ludlam and James Ramm to injury before the break.
Saints, who were beaten at Leicester Tigers six days earlier, already had a lengthy injury list going into the game.
And they found themselves behind after just five minutes as Quins won a breakdown penalty in their own half, allowing them to work their way upfield.
And when Danny Care took a quick tap from another penalty, Quins were in business, moving the ball quickly before Cadan Murley overpowered Alex Mitchell to score.
Marcus Smith missed the conversion and Quins were made to pay as Saints mounted an attack at the other end.
A scrum penalty allowed George Furbank to kick into the 22, and Saints worked a slick lineout move that ended when Sleightholme, making his first start since February, flew over with a trademark fine finish.
Furbank added the extras to give Saints the lead, and the fly-half soon made a huge hit on Andre Esterhuizen to put the hosts on the front foot again.
However, Quins held out and they were always a threat on the counter, with Care doing some dazzling work to put Saints under real pressure in their own 22.
It took a huge tackle from Furbank on Esterhuizen and a trademark Courtney Lawes turnover on his own line to relieve the pressure for Saints.
But it was only a temporary reprieve as more loose play in the Quins half invited more counter-attacking opportunities, and when the away side won a couple of penalties, they kicked to the corner and rumbled over through hooker Jack Walker.
Smith converted to put Quins 12-7 up, but Saints were handed a gift at the other end as the away side overthrew a lineout, allowing Lawes and Tom Pearson to combine to send Ludlam over.
Furbank converted and Saints had their lead back, but they lost skipper Ludlam, who bravely tried to battle on after taking a knock but he was eventually forced off.
Ramm quickly followed his skipper off the field as he was helped off by the medics, meaning Saints had suffered two huge injury blows before the break.
But there was a huge boost for the home side as Mitchell picked Care's pocket at a Quins scrum inside the 22, kicked ahead and then grabbed the ball to score.
Furbank converted with the final kick of an action-packed first 40 minutes, and the fly-half, who was having a fine night, was on target with a penalty two minutes into the second period.
But Quins quickly hit back with some patient play, resulting in lock George Hammond diving over out wide.
Smith added the extras with aplomb before Saints tried to apply some pressure at the other end of the field, but the home side were still struggling to get the ball to go to hand.
The lack of ball security from Saints was allowing Quins to get out, and the home side were wasting chances, none more so than when Tom Litchfield charged for the line but saw Quins get over the ball to win a penalty.
But when Saints did find their feet, with a penalty coming, they pieced together a fine move that ended with Alex Coles juggling the ball before diving over to bag the bonus-point try.
Furbank converted to make it 31-19 but there were still more than 15 minutes to play and Saints were beginning to concede penalties in defence.
The home side just couldn't find a way out and the inevitable happened when Will Evans powered over.
Smith converted to cut the gap to five points with 10 minutes remaining, but Saints were threatening every time they got into the away half.
And after George Hendy turned on the turbos, the full-back sent Sleightholme in out wide for a try that drew a roar from the home fans.
Furbank missed the conversion and Quins were straight back at it, and only a sensational last-ditch intervention from Lawes stopped the away side scoring.
Saints thought they would stop Quins getting back to within losing bonus-point range when the away side knocked on, but Mitchell threw an intercept pass on his own line and replacement hooker Jibulu eventually forced his way over.
Smith converted and there was still time for the restart, with nerves now really jangling at the Gardens.
But Saints trapped Quins in their own 22 before eventually closing the door as the home supporters celebrated a huge success.
Saints: Hendy; Sleightholme, Freeman, Dingwall, Ramm (Litchfield 38); Furbank, Mitchell; E Waller (A Waller 58), S Matavesi (Cruse 74), Davison (Millar Mills 58); Munga, Coles; Lawes, Pearson, Ludlam (c) (Scott-Young 38).
Harlequins: Green; Murley (Beard 71), Joseph, Esterhuizen, Lynagh (Evans 74); Smith, Care (Porter 70); Baxter (Garcia Botta 65), Walker (Jibulu 60), Lewis (Chawatama 65); Herbst (Cunningham-South 60), Hammond; Lamb, Evans, Dombrandt (c).
Referee: Sara Cox