Champions Cup: Glasgow Warriors sat bottom of Pool 3 and pointless after an opening 19-28 defeat at home to Northampton Saints. However, a first half try from No.8 Ally Miller was followed by McKay’s flying effort as the visitors took a one-point 12-11 win.
Aviron Bayonnais’ replacement outside centre Reece Hodge had two penalty opportunities to kick the winning points but sent both efforts wide.
After a close opening, the hosts were handed an advantage when Glasgow Warriors tight-head prop Zander Fagerson was shown a yellow card for an infringement.
Aviron Bayonnais then took a 29th-minute lead as fly-half Camille Lopez put his side ahead.
The hosts put mounting pressure on their 14-man visitors and after initially being held up moments later hooker Facundo Bosch scored the opening try at the back of a driving maul, unconverted by Lopez.
Glasgow Warriors responded on 37 minutes when the ball was played out wide for Miller who sprinted past two covering defenders to score, converted by fly-half Ross Thompson to bring his side back to 8-7 at half-time.
With little to separate the sides, Lopez took his opportunity to kick a 49th-minute penalty to give his side a four-point lead
Glasgow Warriors were rallying metres from the try-line, desperate for an away victory before playing out wide for full-back Josh McKay, who, with a flying dive, was judged to have just grounded the ball by the TMO on 56 minutes.
With his side a point behind, replacement Hodge had the opportunity to hit back for Aviron Bayonnais but sent his long-range penalty wide.
Then, with the clock ticking even closer to the red, Hodge went for another penalty effort from range. Despite having the distance, his kick was narrowly wide again.
Aviron Bayonnais threw everything forward late, but their Scottish visitors held on for a vital win.
Glasgow Warriors head to Exeter Chiefs in the third round of fixtures in January, while Aviron Bayonnais head to Northampton Saints.
Scorers:
Aviron Bayonnais: Try: Facundo Bosch. Penalties: Camille Lopez (2).
Glasgow Warriors: Tries: Ally Miller, Josh McKay. Conversion: Ross Thompson.
Teams:
Aviron Bayonnais: 15 Tom Spring, 14 Aurélien Callandret, 13 Cheikh Tiberghien, 12 Guillaume Martocq, 11 Nadir Megdoud, 10 Camille Lopez, 9 Gela Aprasidze, 8 Rodrigo Bruni, 7 Baptiste Heguy, 6 Rémi Bourdeau, 5 Manuel Leindekar, 4 Denis Marchois, 3 Junior Tagi, 2 Facundo Bosch, 1 Swan Cormenier. Replacements: 16 Vincent Giudicelli, 17 Matis Perchaud, 18 Tevita Tatafu, 19 Thomas Ceyte, 20 Arthur Iturria, 21 Maxime Machenaud, 22 Thomas Dolhagaray, 23 Reece Hodge.
Glasgow Warriors: 15 Josh McKay, 14 Kyle Rowe, 13 Huw Jones, 12 Sione Tuipulotu, 11 Ollie Smith, 10 Ross Thompson, 9 George Horne, 8 Ally Miller, 7 Tom Gordon, 6 Gregor Brown, 5 Alex Samuel, 4 Greg Peterson, 3 Zander Fagerson, 2 George Turner, 1 Jamie Bhatti. Replacements: 16 Angus Fraser, 17 Nathan McBeth, 18 Oli Kebble, 19 Richie Gray, 20 Max Williamson, 21 Henco Venter, 22 Ben Afshar, 23 Tom Jordan.