He really needed to double up in the Olympic distance events, he said, because he'd dedicated the medals to his unborn twins.
"These two gold medals mean the world to me, because my wife is carrying twins," Farah said. "I didn't want to have just one gold medal, and then have twins."
Roared on again by a boisterous, capacity crowd at the 80,000-seat Olympic Stadium, Farah surged ahead late and held on Saturday night to win the 5,000 metres in 13 minutes, 41.66 seconds. The Somali-born Farah won the 10,000 metres on Britain's "Super Saturday" last weekend, the same night Jessica Ennis won the heptathlon and Greg Rutherford the long jump.
This Saturday, it was entirely Mo's moment. He still had the energy to do a few playful sit-ups on the track before he grabbed a British flag for the real celebrations.
Almost nobody left the stadium until Farah was presented with his gold medal and the British anthem echoed around Olympic Park again.
"It's unbelievable," the 29-year-old Farah said. "Two gold medals, who would have thought that?"
Farah was under intense pressure coming into the London Games, with Britain expecting him to deliver a gold medal. He went one better, and now even has British athletics greats like Seb Coe describing him as "arguably the best British runner of all time."
He even had Usain Bolt impersonating the Mobot, his trademark victory celebration.
Bolt put both hands on his head in the shape of an M just after crossing the finish line as he anchored the Jamaican 4x100-meter relay team to gold in a world record time. It was Bolt's third gold medal of the games, repeating his sprint triple from Beijing.
The pair joked together for the crowd long after the last event on the track at the London Games was finished.
"Massive respect for Usain, he did a Mobot," Farah said. "Usain Bolt is a legend. For what he does for the sport, absolutely amazing.
"To do the Mobot, I can't believe he did that."
Bolt said he liked it so much he might use it some more.
"I said I was going to do that before the Olympics. It slipped me there the first two times because I was so happy," he said of his celebrations for the 100 and 200 gold medals. "But I watched his 5,000 before I came out. Then I thought, 'Oh yes. Me and Mo go way back."
Bolt is undoubtedly the star of the Olympics, but Farah's double will long live on British folklore.
Farah was the seventh man to win both the 5,000 and 10,000 titles at a single Olympics, the first from Britain. He was also the first man to win the Olympic 5,000 title as the reigning world champion.
He took the lead with 700 metres to go, staved off all challenges and, riding constant screams of encouragement, swept away on the home straight. He crossed the finish line with his arms up in triumph, then slapped his bald head and dropped to his knees.
Dejen Gebremeskel finished strongly to earn silver for Ethiopia in 13:41.98, and Thomas Longosiwa of Kenya took bronze in 13:42.36.
After his little demonstration of situps, Farah grabbed a Union Jack and took off for a victory lap.
He found his wife, Tania, who is pregnant with twins, and daughter Rhianna in the crowd and hugged them.
Farah, who was born in Somalia and arrived in Britain when he was 8, gave plenty of thanks.
"I want to thank everyone who has supported me, all my coaches from the past, all the people who have been part of my life, particularly my wife," he said. "Her carrying twins, it hasn't been easy. It's been a long journey of grafting and grafting."
With such crowd support for Farah, the other runners barely stood a chance.
"The crowd helped him. He ran 100 per cent and they added another 10," said American runner Bernard Lagat, who finished fourth. "Everybody knew he was the favourite. I knew it. All 15 runners knew it. We were going to run against the favourite guy, he was the greatest of all."
U.S. runner Galen Rupp trains with Farah and finished second to him in the 10,000. He had a charge at the lead late in the 5,000 but faded to finish seventh, watching as his friend crossed the line first.
"Mo, he's great. Obviously a lot of pressure on him," Rupp said. "He's so well-equipped to deal with that. His personality is so laid back. I'm thrilled for him. It really couldn't happen to a better person."