Faizulin, appearing in only his second international after making his debut in last month's friendly against Ivory Coast, put the home side ahead with a fine strike on the half-hour in Capello's first competitive match in charge.
"I think we could have scored more but 2-0 is not too bad also," the Italian, who replaced Dutchman Dick Advocaat as Russia coach last month following their disappointing showing at Euro 2012, told a news conference.
"We were a bit tight in the first 15-20 minutes but then played much better. In general, we didn't have any problems tonight, so I'm pleased with the team's performance."
The Russians totally dominated for the first hour but were guilty of missing several chances to add to their tally.
Striker Alexander Kerzhakov alone wasted a handful of good opportunities. He also hit the post with a free-kick from the edge of the box minutes before Shirokov wrapped up the points with a 78th-minute penalty.
The midfielder calmly slotted home from the spot after defender Craig Cathcart was harshly judged to have pushed Alexander Kokorin inside the box.
The visitors, ranked 116 positions below 13th-placed Russia in the FIFA standings, rarely got out of their half and had only one effort on goal - a Gareth McAuley header that was cleared off the line.
It was the first competitive match for Michael O'Neill at the helm of Northern Ireland following three friendlies and he was disappointed by the display.
"We're disappointed to lose the game. We were disappointing in our possession at times. We had to work so hard off the ball," he said. "As for the penalty, I don't think it should have been called."
Russia's win maintained their unbeaten record against Northern Ireland, who managed two draws and two defeats in four World Cup and European Championship qualifiers against the former Soviet Union.
