London Scottish were aiming for a third straight win as they prepare to take the seismic step of going full-time next season.
With five seconds played, Scottish winger Williams caught the ball on the full from the kick-off and scampered over in the right corner with the Carnegie defence still half asleep.
Perhaps there is something in the water in these parts – Lee Blackett claimed the fastest try in Premiership history when he scored for Carnegie in a memorable home win over Newcastle at Emerald Headingley in March 2008.
After the shock of conceding so early on, Lowes’ men soon awoke from their slumber and tries from No8 Richard Beck and scrum-half Ollie Fox quickly put them in control. They added a third before the break through hooker Mike Mayhew, but could not find a fourth to secure the bonus point as Scottish roused themselves in the second half to hit back with two more tries of their own to ensure a tense finale.
Stevie McColl, Callum Irvine, Charlie Beech, Mayhew, Jack Whetton Charlie Capps and Ben West all made their final appearances for Carnegie, who ended their Greene King IPA Championship campaign in sixth spot.
Head coach Lowes said: “It was a disappointing start, but we didn’t let it affect us and dominated most of the game, although I was a bit disappointed we didn’t get another try.
“A number of lads have been told they are leaving, but their attitude has been fantastic and I must thank them for their efforts.
“They have not shirked one training session and they have been outstanding. I wish them all the best in whatever they now choose to do.”
After Williams’ rapid opener, Beck, who became only the seventh player in the club’s history to make 100 league starts for Carnegie, plunged over the line inside the left channel before a delightful score from Fox.
Carnegie centre Andy Forsyth drove at the heart of the Scottish defence and showed intelligence to send the supporting Fox scampering under the posts.
McColl’s two conversions put Carnegie 14-7 ahead and they began to dominate field position, despite the disruption of Beck being forced off for a head injury assessment. A third try arrived when Mayhew rumbled over the line from close range and McColl’s third conversion made it 21-7 at the break. Scottish dug deep in the second half but chances grew scarce until visiting full-back Craig Holland intercepted a home pass close to his own line and raced almost the length of the field to score.
After Holland’s try was converted, Scottish scored again when No8 Danny Kenny went over to make it three tries apiece but the hosts held on.
Yorkshire Carnegie: Elder, Mann (Davey 75), Forsyth, Bullough (Wilson 72), McColl , Irvine (Davey 52, Irvine 63, Newborn), Fox, Beech (Thraves 63), Mike Mayhew, Mitchell (Capps 79), Whetton (Lloyd 60), Smith, Bainbridge, Richard Mayhew, Beck (West 20)
London Scottish: Holland, Stevenson, Neal, Lyle (George, 72) Williams, Atkins, Hoadley (Alex Walker 50), Harris (Onyeama-Christie 60), Miller (Hayhow 72), McQuillin (Cringle 40), Milne, Gillanders (Eliet 69), Atkinson, Chris Walker (Marley 63), Kenny
Referee: Simon Harding