Michael Phelps won his preliminary heat for the 400-meter individual medley this morning, but his time barely qualified him for tonight's finals. He goes into the evening finals seeking his first of a possible seven gold medals at his last Olympic Games.His time of 4:13.33 was only good enough for the eighth seed and he will have an outside lane. Chief rival Ryan Lochte is the third seed after swimming 4:12.35 in the prelim.The first full day of competition opened with the prizefight match-up of Phelps versus Lochte, battling not just for the 400 IM crown but ultimately, swimming's top dog.Phelps, the most golden Olympian ever, begins his fourth and final Games with his toughest challenge, the grueling event considered swimming's decathlon. While Phelps is the world record holder, having first broken it in 2002 and keeping it ever since, he was beaten by Lochte the last time they faced off in it, in the Olympic qualifying trials just over a month ago.Lochte, the Florida-based swimmer who has been declaring London his time to emerge from Phelps' long shadow, has been the fastest 400 IM swimmer this year, swimming it in 4 minutes 7.06 seconds at the trials in Omaha. Phelps came in second at 4:07.89, also the second fastest in the world this year.With echoes almost still ringing of the Paul McCartney-led sing-along to "Hey Jude" that concluded Friday night's Opening Ceremonies, crowds began lining up Saturday morning at the for the preliminary heats that kickoff the swimming competition.The rest of this morning's heats are for the women's 100-meter butterfly, the men's 400-meter freestyle, the women's 400-IM, the men's 100-meter breaststroke and the women's 4x100 freestyle relay.Medals will be awarded in the evening in the 400-meter events.