Warriors went toe-to-toe with the reigning Gallagher Premiership champions and were unlucky not to take at least a point from an exhilarating contest.
A disallowed try from Sione Vailanu, which would have been his second of the night, midway through the second half, proved a pivotal moment.
Referee Christophe Ridley’s on-field decision was a try but TMO Rowan Kitt suggested that the Tongan number eight had grounded the ball before the line and then knocked it on.
The try, which would have levelled the scores at 19-19, was chalked off and with it went Warriors’ chances of victory.
Harlequins were down to 14 men at the time after Danny Care had been sin-binned for a deliberate knock-on but they scored the only points of that ten minute period when Tommy Allan slotted a penalty to put Warriors out of bonus point range.
Harlequins secured their try bonus point when Tom Lawday crashed over from close range four minutes from time but Warriors were game to the last.
Seb Atkinson marked an excellent first Premiership start with a try a minute from time and although Billy Searle took the conversion quickly with a drop kick, there was not quite enough time for Warriors to work their way upfield for another score which would have secured at least one point.
Atkinson did not look out of place against Harlequins’ powerhouse Andre Esterhuizen and was part of a backline comprised entire of current or former academy players.
They held their own against a more experienced Harlequins back division but Warriors encountered problems in the tight and were heavily penalised at the scrum which meant attacking opportunities in the second half were limited.
Steve Diamond’s side tackled heroically and ferociously at times but having turned around with the scores at 14-14 for the second successive Friday, it was not quite enough to force a win.
Noah Heward marked his return to action after almost four months out with a broken ankle with a try after 18 minutes, rounding off a sustained attack with try that Fin Smith converted from the right touchline.
Harlequins were level again six minutes when Tyrone Green capitalised on a slip from Heward to score a try converted by Will Edwards and they went ahead just before the break when Care scored after Hugh Tizard had galloped through the middle.
But Warriors made a penalty advantage count in the last minute of the half and patiently built the pressure before Vailanu powered over for his second try in as many matches.
Smith’s conversion levelled the scores again and meant it was all to play for in the second-half but it was Harlequins who scored next when number eight Archie White crossed from close range.
Vailanu’s claims for a second try were then overturned although Harlequins had a try disallowed at the other end when replays showed that Matas Jurevicius was held up over the line.
Jurevicius was denied again by a superb covering tackle from Alex Hearle but Warriors struggled to get out of their 22 and Lawday capitalised for the score that eventually broke Warriors’ resistance.
Warriors | 15 Noah Heward (Searle 60), 14 Perry Humphreys, 13 Oli Morris, 12 Seb Atkinson, 11 Alex Hearle, 10 Fin Smith, 9 Gareth Simpson, 1 Murray McCallum (Waller 53), 2 Niall Annett (Miller 63), 3 Christian Judge (Tyack 63), 4 Matt Garvey (A Kitchener 53), 5 Graham Kitchener (Clegg 53), 6 Joe Batley, 7 Ted Hill (C), 8 Sione Vailanu.
Replacements | 16 Isaac Miller, 17 Ethan Waller, 18 Jay Tyack, 19 Andrew Kitchener, 20 Justin Clegg, 21 Will Chudley, 22 Billy Searle, 23 Tom Howe.
18m | Heward try 5-0
19m | Smith con 7-0
24m | Green try 7-5
25m | Edwards con 7-7
35m | Care try 7-12
36m | Edwards 7-14
40m | Vailanu try 12-14
40m | Smith con 14-14
51m | White try 14-19
67m | Allan pen 14-22
76m | Lawday try 14-27
77m | Allan con 14-29
79m | Atkinson try 19-29
80m | Searle con 21-29