But Miller, a former world junior champion, is just 22. Felix is 30 and increasingly troubled by injuries. She surely knew that Miller was going to be an even bigger threat in Rio de Janeiro, and Miller indeed had a sizable lead down the final straightaway Monday.
Felix â easy to recognize in Lane 4 in her high compression socks â quickly moved up from third to second as Millerâs stride started to shorten. Felix then surged alongside Miller as both closed on the line. It appeared Felix was just pushing in front when Miller fell forward, both arms extended, like a beach volleyball player diving desperately to keep a rally alive.
âWhat was in my mind was, I had to get a gold medal,â Miller said. âThe next thing I knew, I was on the ground.â
Grimacing as she pitched forward, she landed on her chest on the blue track and then rolled onto her back and stayed that way for several minutes, chest heaving as the unofficial result became official and someone handed a Bahamian flag to her as she remained supine.
Felix, who had come across the finish line upright, was soon lying on the track for an extended period, too, as she tried to recover.
Millerâs time of 49.44 seconds, a personal best, gave her the gold. Felixâs time of 49.51 meant silver: quite a blow to a woman who once planned to chase a 200-400 double in Rio in what is likely to be her final Olympics.
Felix failed to qualify for the Games in the 200, missing out on the United Statesâ third spot when, while running on a sore ankle, she was beaten across the line by Jenna Prandini at the Olympic trials in Eugene, Ore., last month.
Prandini also fell forward at the finish, and like Miller, she said her dive had not been intentional.
âBut Iâm happy that it happened because it got me third,â Prandini said at the time.
Miller was certainly not complaining, either. Dives in other sports have negative connotations, including the sport that Brazilians hold dearest, which is also the sport usually played at the Olympic Stadium.
But track and field is not soccer, and at least for now the rules allow a runner to leave her feet as she crosses the line.
âWe do continue to look at our rules to make sure they are current,â said Chris Turner, a spokesman for the I.A.A.F., trackâs world governing body. âIf we start seeing a pattern of these sorts of things, weâd look at that. But itâs first across the line, not the first across the line in the most graceful way. Itâs very well policed what crossing the line means.â
Although there was plenty of general public confusion Monday night, it also does not matter if a runnerâs feet or hands or head cross the line ahead of an opponent. The finish order is determined by when a runnerâs torso crosses the line, and the photo at the finish Monday night left no room for debate.
If Felix had leaned at the line, it might have made a difference. If Miller had run through the line herself, she still might have won.
âSprinters know the quickest way across the line is a well timed lean,â Michael Johnson, a former Olympic 200 and 400 champion, wrote on Twitter late Monday night. âTrust me on that.â
The research is clear: Once you leave your feet, you start decelerating faster than if you keep striding and pushing off. But the initial propulsion forward can still make the difference at the finish line, even if it is so tricky to time it just right and also rather painful upon completion (an Olympic track is an abrasive surface).
âIâve never done it before,â Miller said. âI have cuts and bruises, a few burns. It hurts.â
No doubt, but surely not as much as Monday nightâs result hurt, and will continue to hurt, Felix. She has been one of the great sprinters and Olympians of the 2000s, and she will now leave Rio without the career-capping satisfaction she was chasing: a second individual gold medal to go with her 200 victory in London in 2012.
She still has a fine chance at gold with the American 4×400-meter relay team and could well come back, if she stays healthy and hungry, to win another title at the world championships in London next year. But Felix knows that in her country, at least, the public tunes in to track and field only every four years. She knows, too, that this was not nearly the Olympic season she dreamed of when she successfully lobbied the International Association of Athletics Federations and the International Olympic Committee for a schedule change to make the 200-400 double possible.
But at least Bahamians, whose Caribbean nation has only about 380,000 inhabitants, can celebrate, and perhaps it is only right that they get the chance. In 2008, in the menâs 400, the American sprinter David Neville dived â intentionally, in his case â across the finish line to snatch the bronze medal away from another sprinter.
That other sprinter was Chris Brown, who runs for the Bahamas.