Tonight is Michael Phelps' penultimate Olympics event, his last individual one, and the one in which he faces a competitor who, rather than he, holds the world record. The race is televised live in prime time tonight on NBC, and the audience ought to be huge.

And if Phelps wins tonight, tying the single-Olympics gold haul of swimmer Mark Spitz in 1972, the audience for Saturday night's final Phelps appearance -- as part of the U.S. team's 4x100m relay -- ought to he huger. Maybe even hugest.

It's amazing, what this young man has done in this first week of the XXIX Summer Olympics. He's been great, truly. And so have his teammates. He has a chance to match Spitz's total tonight only because his fellow swimmers beat the odds, and the favored French team, to win gold in an earlier relay.

Four years ago, Michael Phelps graciously gave up one of his Olympic relay spots to U.S. teammate Ian Crocker, who ended up earning a gold medal in that event. This year, Crocker has the world record in the 100m fly, and he and Phelps compete tonight. Should Crocker win, then he, not Phelps, has first dibs at completing the team in tomorrow's relay race -- but could, as Phelps did in 2004, surrender his spot, thus giving Phelps a chance to tie Spitz's record tomorrow if he fails tonight.

But if Phelps beats Crocker tonight, then the seventh is his, and so is the spot on the relay team to try for his eighth as part of the U.S. team. Either Phelps pulls off his most amazing finish yet, or Crocker makes some history of his own by beating the most honored athlete at this Olympics.

Either way, how can you not watch?