Two years ago on Court 1 at Wimbledon, Andy Roddick lost a match he should have won. Wednesday evening on that very same patch of grass, the newly-married American won a battle he very easily could have lost.

In a riveting, rousing affair matching former world No. 1s and Grand Slam champions, Roddick nipped Australian star Lleyton Hewitt, 6-3, 6-7 (10), 7-6 (1), 4-6, 6-4, in 3 hours and 50 minutes. The richly-deserved triumph carries the No. 6 seed into the “Andys Mountains” for a battle with a lad named Murray on Friday. Just as importantly, the victory wipes away the bitter taste of one of the most searing defeats in Roddick’s very successful career.

To understand the magnitude of this close-shave escape for Roddick against a longtime rival, you have to go back to the 2007 edition of The Championships. Roddick–in the very same quarterfinal round–took a two-set lead on France’s Richard Gasquet, and served for a semifinal appearance at 5-4 in the third. But Gasquet improbably broke Roddick, pulled out the third set, and raced home with the final two sets to win in five and leave a 24-year-old Roddick reeling. The force of that loss was so substantial that the 2003 U.S. Open champion did not make the semis at another major tournament until this year’s Australian Open. With the ascendancy of Rafael Nadal and the emergence of both Murray and Novak Djokovic on the ATP Tour, the past few years have marked lean times for Roddick, who–through 2005–was a player who could be counted on to play deep into Wimbledon and face Roger Federer in the semis or the final.

The Gasquet loss was damaging in and of itself, but that match had another adverse effect which Roddick simply couldn’t control. Critics have lost sight of the fact that other players have gotten better in recent years. Pundits–instead of viewing Roddick as a modestly-talented man whose hard work has carried him to considerable heights–have chosen to wonder why Roddick hasn’t appeared in more major finals or scored big wins against the likes of Federer and Nadal. In truth, Roddick has continued to squeeze every ounce of talent at his disposal; his only sin is losing to the top few players on the planet.

Because of the negative scrutiny that would automatically attach itself to any of Roddick’s losses–particularly at the slams–the American, who has rarely been afraid to disguise his emotions at press conferences or on the court, internalized the stress and pressure that began to rain down upon him. At least, that’s what his 2007 and 2008 tennis seasons indicated. Drifting through a period of doubt, Roddick knew he had to make a change, and in November of last year, a struggling player offered a man named Larry Stefanki the chance to retool a career in need of a boost.

Stefanki has established himself as one of the top coaches in men’s tennis. Having worked with John McEnroe toward the end of his career, Stefanki then tutored another pair of world No. 1s, Chile’s Marcelo Rios and Russia’s Yevgeny Kafelnikov, in the late 1990s. Earlier this decade, Stefanki molded Chilean Fernando Gonzalez into the 2007 Australian Open runner-up, and was coaching Gonzalez when Roddick dialed his number. Stefanki was persuaded to make the change, and the results have vindicated the decision-making instincts of both player and coach.

Roddick, under Stefanki’s guidance, lost 15 pounds. That fact alone has made the American a fitter, faster player with better defensive skills and superior endurance. Those qualities–not seen in older incarnations of Roddick–helped the flailing 24-year-old of 2007 morph into a confident marathon man of 2009. More to the point, those qualities enabled Roddick to return to the late rounds of major tournaments. The top-ranked player in America reached the semis of this year’s Australian Open, before posting the best French Open showing of his career (the fourth round). Yet, as much as Roddick had to be encouraged by what he achieved in Melbourne and Paris, this act of survival against Hewitt has to rate as an even more redemptive moment.

Roddick cried at the end of this victory for many reasons, but one likely source of the American’s emotional outpouring was that he beat Hewitt at the Australian’s own game. Very simply, Roddick’s fitness won him this match.

On Wednesday, the 26-year-old Roddick and the 28-year-old Hewitt were battling just as fiercely as they had in the past, with the Australian refusing to fold the tent after losing the first and third sets. An unyielding effort allowed Hewitt to win the second and fourth sets, pushing the quarterfinal collision to a deciding stanza before an enraptured English audience. Normally, a fifth set is Hewitt’s domain; the Aussie entered this match 29-13 in five-setters, an unsurprising fact given Hewitt’s identity as the man who would never lose a tennis match due to physical limitations. Hewitt built his game and his reputation on conditioning and stamina; you’d always have to hit several extra balls to win points offf Hewitt, and usually, he’d run down more balls than opponents could throw at him. In the 2001 U.S. Open, Hewitt and Roddick–then 20 and 19 years old, respectively–locked up in a contentious quarterfinal under the lights in New York. The two men traded punches deep into the night, but in set number five, Hewitt owned the fresher legs and more positive body language. It was just one of many times when the diminutive Australian wore down a forceful foe. Without his peak fitness level, Hewitt never would have attained a fraction of what he ultimately did as a tennis pro.

How sweet it must have been, then–achingly sweet, in fact–for Roddick to turn the tables and beat Hewitt with his own fresher legs. The American–having saved break points with big serves in the early part of the fifth set–ultimately broke Hewitt at 4-all by running down shots. Roddick’s court coverage, combined with a reliable two-handed backhand, surprised Hewitt on a break point, and when the Aussie could only hit a tame half-volley off an attempted Roddick passing shot, the American raced toward the net and put away an easy forehand to grab a 5-4 lead.

Once again given the chance to serve out a Wimbledon quarterfinal at 5-4 on Court 1, Roddick didn’t crack under pressure. Hewitt did get to 30-all, but a forehand approach shot and a well-struck passing shot gave Roddick the final two points he needed. After three Wimbledons with premature exits, Andy Roddick battled back to the semifinals with the kind of lunch-pail persistence… and the help of 15 recently-shed pounds.

It’s true in many more ways than one: Andy Roddick is losing baggage. No longer weighted down physically or mentally, this mainstay of the top 10 is back where he belongs at the Big W. If he can derail the other Andy in Friday’s semis, Roddick will find himself competing for his first-ever Wimbledon championship.