Quins pull Wasps' sting
Wasps, suffering only their second Premiership defeat in their last six matches, had only themselves to blame as veteran England back row forward James Haskell and mercurial flyhalf Danny Cipriani were sin-binned.
The points from Philippines-born Smith, and tries by Marland Yarde and Charlie Walker, edged the match the visitors way.
However, Wasps, losing finalists last season to Exeter, did move into second spot thanks to a bonus point.
They too scored two tries through the prolific Christian Wade and Tom Cruse – Cipriani contributing 11 points with the boot.
For Harlequins, who moved into fifth spot, it was their first away win since beating Gloucester in March.
Christian Wade and Tom Cruse touched down for the home side but Marcus Smith knocked over two late penalties to edge his side over the line.
Smith kicked two penalties either side of Wade’s try as the winger completed a fine backs move involving Marcus Watson and Willie Le Roux.
The second Smith penalty came after James Haskell was sent to the sin bin for an off-the-ball incident with Joe Marler.
Harlequins used of their extra man as Smith’s exquisite crossfield kick was knocked back by Mike Brown and Yarde put the visitors ahead 11-10.
But Wasps, back up to 15, were back in front before the break through a Cipriani penalty, as he took his points tally for the club beyond 500 points.
Harlequins restored their advantage early in the second half as Joe Marchant broke down the short side before feeding Walker who dived over to make it 18-13.
The scores were level after 55 minutes though as hooker Cruse was at the back of a successful driving maul for his first Premiership try after Kyle Sinckler had been shown a yellow card.
Cipriani knocked over his third penalty of the afternoon but he then became the third man to be shown a yellow card after being adjudged to have deliberately knocked-on.
Two penalties for Smith in the final moments gave Harlequins the victory.
The scorers:
For Wasps:
Tries: Wade, Cruse
Cons: Cipriani
Pens: Cipriani 3
For Harlequins:
Tries: Yarde, Walker
Con: Smith
Pens: Smith 4
Yellow cards: Marcus Smith (Wasps, 19), Marcus Smith (Wasps, 65), Kyle Sinckler (Harlequins, 52)
Teams:
Wasps: 15 Willie Le Roux, 14 Christian Wade, 13 Elliot Daly, 12 Gaby Lovobalavu, 11 Marcus Watson, 10 Danny Cipriani, 9 Joe Simpson, 8 Nathan Hughes, 7 Guy Thompson, 6 Alex Rieder, 5 Will Rowlands, 4 Joe Launchbury (captain), 3 Jake Cooper-Woolley, 2 Tom Cruse, 1 Matt Mullan.
Replacements: 16 Ashley Johnson, 17 Simon McIntyre, 18 Marty Moore, 19 Marcus Garratt, 20 James Haskell, 21 Craig Hampson, 22 Rob Miller, 23 Juan De Jongh.
Harlequins: 15 Mike Brown, 14 Marland Yarde, 13 Joe Marchant, 12 Jamie Roberts, 11 Charlie Walker, 10 Marcus Smith, 9 Danny Care, 8 Mat Luamanu, 7 Jack Clifford, 6 Chris Robshaw, 5 James Horwill (captain), 4 George Merrick, 3 Kyle Sinckler, 2 Dave Ward, 1 Joe Marler.
Replacements: 16 Elia Elia, 17 Mark Lambert, 18 Will Collier, 19 Ben Glynn, 20 Archie White, 21 Dave Lewis, 22 Tim Swiel, 23 Harry Sloan.
Referee: Andrew Jackson
Assistant referees: Anthony Woodthorpe, Paul Dix
TMO: David Rose
Round 3 results 👇
Full table 👀
It was another electric weekend of @premrugby action… pic.twitter.com/ymaWKaJIS3
— BT Sport Rugby (@btsportrugby) September 17, 2017