Welsh's hopes were severely hampered when Runciman saw yellow
Grenoble jumped to the top of Pool Five in the European Challenge Cup as they secured a hard-fought win over London Welsh at the Stade Lesdiguieres in Friday.
The home side overtook fellow French outfit Stade Francais Paris ahead of their clash with I Cavalieri Prato Saturday thanks to a 20-9 success over the English-based European debutants.
The contest was even closer than the scoreline suggests, however, with Grenoble only pulling clear through a converted try from lock Andrew Farley with just four minutes remaining.
Farley's late effort ended the Exiles' stubborn resistance after they threatened a second successive European Challenge Cup away victory.
The sides were tied 6-6 at half time after Clement Darbo and Aled Davies exchanged a brace of penalties and it was the visitors who struck first in the second period as Davies slotted another three pointer after 47 minutes.
But Grenoble seized the initiative just three minutes later when hooker Vincent Campo crossed for the first of their two tries.
Darbo's conversion made it 13-9 yet London Welsh built plenty of momentum and could have retaken the lead had Davies not been off target with penalty attempts in the 62nd and 64th minutes.
London Welsh's hopes of the win that would have given their own quarterfinal qualification efforts a huge boost were severely hampered when scrumhalf Nick Runciman saw yellow on 76 minutes and Grenoble took advantage of the extra man as Farley powered over moments later.
Tries: Campo, Farley
Cons: Darbo, Hart
Pens: Darbo 2
For London Welsh:
Pens: Davies 3
Yellow card: Nick Runciman (London Welsh, 74)
Grenoble: 15 Joaquim Tuculet, 14 Viliame Waqaseduadua, 13 Rida Jaouher, 12 Aloisio Butonidualevu, 11 Florian Ninard, 10 James Hart, 9 Clement Darbo, 8 Flavein Nouhaillaguet, 7 Jonathan Best, 6 Fabien Alexandre, 5 Andrew Farley, 4 Thibault Rey, 3 Lotu Taukeiaho, 2 Vincent Campo, 1 Romain David.
Replacements: 16 Anthony Hegarty, 17 Gregory FabroN, 18 Karim Kouider, 19 Alexandre Pollard, 20 Valentin Courrent, 21 Henri Vanderglas, 22 Blair Stewart, 23 Fabien Gengenbacher.
London Welsh: 15 Tom Arscott, 14 Phillip Mackenzie, 13 James Lewis, 12 Seb Jewell, 11 Ashley Smith, 10 Alex Davies, 9 Nick Runciman, 8 Daniel Browne, 7 Mike Hills, 6 Lee Beach, 5 Matt Corker, 4 Adam Brown, 3 Arthur Joly, 2 Greg Bateman, 1 Tom Bristow.
Replacements: 16 Willie Hafu, 17 Billy Moss, 18 James Tideswell, 19 Mike Denbee, 20 Jon Mills, 21 Matt Keyte, 22 Simon Whatling, 23 Nick Scott.
Referee Andrew McMenemy (Scotland)
Assistant referees: Peter Allan (Scotland), Adrian Graves (Scotland)