A final-round meltdown by local hope Marc Warren left Singh and Molinari on 17-under 271 and in a shootout for the first prize of 416,660 pounds ($645,000), which the 40-year-old Indian claimed by draining a 15-foot birdie putt on the first playoff hole.
Singh, the son of a former Olympic 400-meter runner, shot a bogey-free 5-under 67 for the joint-lowest round of a grueling final day, when the wind picked up to finally make the Castle Stuart links a genuine test. He then watched on television as first Warren then overnight leader Molinari (72) threw away shots down a tough closing stretch right into the wind.
"I was just enjoying a nice cup of tea and some chocolate cake," Singh said of his hour-long wait for the last groups to finish. "I said to myself that I'd see the finish and then leave for the airport. But as the chocolate cake went down, it got exciting out on the course."
Warren, playing in the penultimate group and also seeking that one remaining berth in the British Open, forged a three-shot lead with six holes remaining but faltered under pressure and dropped four strokes in the final four holes. He finished tied for third with Alexander Noren of Sweden (70) on 16 under, his implosion costing him 275,000 pounds ($428,000).
"It's going to be a long drive home tonight," said Warren, who was being cheered on by Scottish First Minister Alex Salmond. "You don't get many chances to win your national Open.
"I had it in my hands."
Warren's collapse left Molinari back in front as the Italian attempted a wire-to-wire victory after a dominant week in the Scottish Highlands as he tried to emulate his brother Edoardo's Scottish Open win in 2010.
He bogeyed No. 15, though, and needed a 10-foot par-saving putt at the last to force the playoff. Molinari's approach from the middle of the fairway at the first extra hole — No. 18 — landed at the back of the green and his long birdie putt came up well short, leaving Singh an opportunity he didn't pass up.
By winning his first title in more than four years, Singh not only will climb back into the top 100 from his current ranking of No. 192 but will play at the British Open — staged at Royal Lytham & St. Annes starting Thursday — for the only the second time in his 19-year professional career.
"I was going to go back to India and spend some time with the family," said Singh, who claimed his fourth European Tour victory. "I think God has been kind. I'm very fortunate."
After three opening rounds of very low scoring in improbably calm conditions, Castle Stuart finally bared its teeth — something many players asked for ahead of the British Open.
A fierce westerly wind and heavy rain at times proved too much for top-ranked Luke Donald (73) and Phil Mickelson (74), who both finished tied for 16th on 12 under. Only six players of the 77 who made the cut broke 70, with gusts off the Moray Firth forcing players to use an extra two clubs on many shots while the thick rough beside the wide fairways finally came into play.
"To have two good rounds and then to play in some challenging conditions was a plus," said Mickelson, who followed an opening-round 73 with a 64 and a 65. "Players here got a lot out of the week, myself especially."
Warren was on the brink of becoming the first home winner of the tournament since Colin Montgomerie in 1999 but it all started to go wrong on No. 15, which he double-bogeyed after missing his approach shot and three-putting.
After dropping further shots on Nos. 16 and 17, he was consoled off the last green by playing partner Soren Kjeldsen, and looked absolutely distraught.
Warren was one of a handful of players in contention for that final British Open qualifying berth, which was available for the highest non-exempt player finishing in the top five.
Noren, who shared the lead after round two, then wasted a chance to make the playoff when he missed a two-foot par putt on the last, a familiar sight on a day of tension across the links course.
Singh, with his unorthodox swing, held his nerve better than anybody after going through the first six holes in four under, having started the round five shots back in 15th.
His father, Milkha, placed fourth in the final of the 400 at the 1960 Olympics in Rome, only missing out on a bronze medal following a photo finish. The younger Singh said after his round that his dream is to play in the golf tournament at the Rio Games in 2016, when the sport returns to the Olympic program.
Singh went 95 events between his third and fourth victories, having previously won the Austria Open in June 2008. He now needs his management company to find him a place to stay in Lytham for the year's third major.
"It's the icing on the cake," he said.