* Bird wins Saudi season-opener
* Debutants Porsche and Mercedes complete the podium
* Champion Vergne retires from race (Adds details, quotes)
Nov 22 (Reuters) - Britain's Sam Bird won the opening race of the Formula E season in Saudi Arabia for Envision Virgin Racing on Friday, with series debutants Porsche and Mercedes making immediate appearances on the podium.
The 32-year-old fought through from fifth at the start to continue his record of winning in every season of the all-electric championship dating back to the first in 2014/15.
The win was also Bird's ninth in Formula E, the third most of any driver.
Germany's Andre Lotterer finished second for the Porsche team with Belgian Stoffel Vandoorne taking third place for Mercedes -- with Audi claiming bragging rights also as powertrain provider to Bird's team.
The Diriyah circuit on the outskirts of Riyadh hosts a second race on Saturday.
"I think it's the power of the beard that did that," Bird joked over the radio, alluding to his new look for the 14 race season.
"We've done, quite frankly, an amazing job in the off-season.
"Last year was difficult and I went through a little bit of a transformation. A lot of thinking and mental stuff. Physically, I'm fitter than ever before, massive weight loss," he added.
DS Techeetah's French driver Jean Eric Vergne, winner of the last two championships, retired in the pits midway through the race.
Britain's Alexander Sims led the field away from pole position for BMW Andretti but lost the lead to Vandoorne with 15 minutes to go, with Bird following through to go second, and ended up eighth.
Bird then passed the Belgian for the lead and the safety car was deployed when Audi's Daniel Abt crashed into the wall six minutes from the end, with racing resuming for the final two minutes.
Britain's Oliver Rowland was fourth for Nissan with Robin Frijns fifth for Virgin Racing and reigning Formula Two champion Nyck De Vries sixth for Mercedes after starting third on the grid.
"We were not sure what to expect so we gave it our best and P2 is a great way to start and get confidence for the team," said Lotterer. (Writing by Alan Baldwin in London, editing by Toby Davis and Christian Radnedge)