That was the measure of the gap between fourth place and the third automatic qualifying place at Hayward Field as the 30-year-old Merritt - whose preparations have been undermined by a groin injury and who only reached the final as a fastest loser - clocked 13.22sec and Jeff Porter 13.21.
Accompanying Porter to Rio will be Oregon Ducks American Football wide receiver Devon Allen, who won in 13.03, and Ronnie Ash, who was given the same time as Porter.
Looking ahead earlier this week to the possibility of racing in Rio, Merritt said: "If I was to win, it would be ugly - I'd be on the track crying somewhere, because of all the pain, all the suffering, all the depression I went through to get to this point."
Instead the US trials, which have produced such highs and lows down the years because of their arbitrary, unforgiving format, claimed another victim.
“I still feel like I came in third,” said Merritt immediately after a desperately close race which lacked Coburn’s naked Rio ambition realised with victory at US Olympic trialsthe presence of the 2013 world champion David Oliver because of injury.
But later he added: “I’ve come to grips with it.
"Nothing can be worse than being told you’ll never run again, even if you come up a little bit short.
“I’ve won Olympic games, broken the world record.
“Someone else can have a turn, I guess."
Oliver, meanwhile, tweeted: “Devastated I couldn’t run in the final, hurt left hammy in the semi, but that’s part of the game.”
Another former world champion missed the cut behind Merritt as Jason Richardson, winner at the 2011 Daegu Worlds, was fifth in 13.28.
Lagat, who had dropped out of the 10,000m trials in intense heat, seized his second chance to create history by producing a last lap of 52.8sec in a slow race to finish in 13:35.50 ahead of Hassan Mead who managed 13:35.70 and Paul Chelimo who ran 13:35.92.
The former Kenyan, who became a citizen of the US in 2004, has won two Olympic medals over 1500m - bronze in 2000, silver in 2004 - and is also the second fastest in history over that distance.
“There were people going 'you never know how he’s going to perform’", Lagat reflected after his win. “They were saying I’m done and cannot make the team.
"That didn’t sound right to me.”
Lagat, who admitted his failure to make the team for last year’s IAAF World Championships in Beijing had “crushed” him, said his decision to drop out of the 10,000m three quarters of the way through when he realised a top three place was beyond him had saved vital energy in his legs.
Justin Gatlin - just about - showed LaShawn Merritt who was boss in the 200m after the former world and Olympic 400m champion won his heat in the fastest time run so far this year, 19.74.
The world 100 and 200m silver medallist was 0.01 slower than that in the final, but it was enough to earn victory, although Merritt achieved his objective as he finished second in 19.79, with Ameer Webb claiming the third place in 20.00.
Gatlin will now do the 100/200 double in Rio, where many will make him favourite given the recent hamstring problems which prevented defending champion Usain Bolt from completing the Jamaican trials.
Merritt, who is set on a 200/400m double, said: "I still feel like I can run a little faster."
Tyson Gay, the 2007 world 100 and 200m champion, was sixth in 20.38 and will not contest an individual sprint in Rio.
Olympic and world champion Christian Taylor earned the right to defend the first of those titles in Rio, although he had to settle for second place on the day with a best of 17.39 behind Will Claye, who won with 17.65.
Chris Bernard earned the third spot with a best of 17.21.
Allyson Felix moved through to the women’s 200m after finishing second in her semi in 22.57 behind winner Tori Bowie who ran 22.27.
Maggie Malone took the women’s javelin title with a best of 60.84, ahead of Hannah Carson who threw 58.19 and Kara Winger who registered 57.90.