Zubkov, who had already won gold in the two-man bob, went into the second day of competition with the slenderest of advantages, leading the Latvia-1 sled by just 0.04 seconds.
However despite being pushed all the way by Oskars Melbardis and his Latvian crew during the third and fourth runs, the 39-year old Russian delivered two faultless displays to finish with a combined time of 3 minutes 40.60 seconds, extending the final winning margin by a fraction to 0.09 seconds.
By completing the bobsleigh double, Zubkov matched a feat managed only once before, by Germany's Andre Lange, who won gold in both events in Turin in 2006.
“We have no emotions left after these two runs,” said a visibly drained Zubkov. “We gave all we had for this fourth run as the Latvians were very quick and came really close to us.
“They kept us under serious pressure but luckily, we managed to avoid serious mistakes and kept our lead,” he added.
Hard to beat
Latvia’s pilot Melbardis was delighted with his team’s performance and acknowledged the Russians as worthy winners.
“I'm really happy. It's just four years that I've been in the driver's seat and already won the Olympic silver medal. It's awesome,” he said.
“Of course we tried to get more today but the hosts gave us no chance to overtake them.”
Meanwhile, the USA-1 team, with Vancouver 2010 champion Steve Holcombe in the driver's seat, fought their way onto the podium to take bronze, after finding themselves down in fourth place overnight.
“We came here to win a medal and we did just that,” said Holcombe. “It was a tough and really tight race. We knew Zubkov is really fast; he's a man who is hard to beat.”