One of the great beauties of Davis Cup is that the tournament has been one of the main agents that keeps the game of doubles relevant and intact. Make no mistake, doubles has suffered significantly since the start of the Open era. All you need to do is read the comments at this and other tennis sites to see the degree to which the cult of personality—namely, a fixation with singles stars—has become the main driver of the spectator experience.

Doubles is not only a substantially different game, it lacks the great, perhaps cardinal advantage of singles: It isn’t star driven. You can see just how powerful a factor that is when singles stars deign to play doubles. Why, you could almost sell tickets to doubles when that happens!  
Over the years, even as the working conditions and remuneration for doubles players has improved, the game itself has been whittled down. Once, all the great players played doubles. As the Open era evolved, they began to abandon the game (with some notable exceptions, led by John McEnroe). To some degree, doubles became the domain of specialists. It has also been whittled down at regular tour events; a match tie-break now employed instead of a third set when the teams have split sets. Doubles fans and aficionados can be thankful for the Grand Slams and Davis Cup.  
There’s been a slight shift back the other way, lately, as a number of elite singles players have discovered the joy of doubles, but their participation is sporadic and highly conditional, nothing you could market as a value-added experience.  
Thus, Davis Cup remains the redoubt of doubles. In this, the second most celebrated and truly international competition (after the World Cup of soccer), doubles matters. The game has its own day, Saturday. It’s critically positioned between the two days that each feature singles matches. You can’t win a Davis Cup tie on Friday, but you can do it on doubles Saturday. Even more important, when a tie is deadlocked at 1-1, the doubles becomes critically important. At times, a doubles win can also be the unexpected launch point of a comeback that enables you to survive a near-death 0-2 experience to win.  
Today, the first doubles Saturday of this year’s Davis Cup competition, we had a great demonstration of just how important and unpredictable doubles can be, as well as how doggedly and brilliantly players can perform in doubles when it really matters. It was, all in all, a doubles day for ages. Three teams—Serbia, France, and Argentina—wrapped up clean 3-0 sweeps by winning the doubles, but at the other five ties doubles may fulfill its intended role as a potentially pivotal “swing” match. Let’s take a quick look at them.  

Spain trails at Canada, 1-2: Spain, the latest nation to produce a Davis Cup dynasty, was on the verge of humiliation in Vancouver. Although it was without the services of its top three players, Rafael Nadal, David Ferrer, and Nicolas Almagro, few would have predicted an 0-3 whitewash. That was averted, thanks to thrilling 6-2 in-the-fifth win by Marcel Granollers and Marc Lopez over Canada’s Daniel Nestor and Vasek Pospisil. This struggle featured two of the best doubles players on the planet, Nestor and Lopez.

Now, the heat will be on Milos Raonic to wrap up the tie for Canada with a win over Granollers in tomorrow’s third singles rubber, the clash of the teams’ top players. Raonic will be the heavy favorite, but should Granollers pull off the upset—watch out. Canada’s unheralded No. 2 Frank Dancevic, who upset Granollers in the second rubber, can’t be expected to pull off another miracle.  

Croatia trails at Italy, 1-2: A decisive four-set doubles win by Simone Bolelli and Fabio Fognini over Marin Cilic and Ivan Dodig in a match that lasted three hours and 25 minutes on the slow clay of Turin sets the table or an intriguing, potentially tie-ending match between Italian No. 1 Andreas Seppi and his Croatian counterpart, Marin Cilic. Bear in mind that while Cilic is a far more recognizable name, Seppi has quietly crept into the Top 20, and just weeks ago eliminated Cilic in the third round at the Australian Open.

Brazil trails at United States, 1-2: If you didn’t know better, you might have penciled in a sweep by Team USA after the Friday singles. After all, Bob and Mike Bryan have won 84 doubles titles, a record 13 Grand Slam titles, and they’ve always been dedicated Davis Cuppers. Their record in the competition going into today’s match was 20-2. As if you needed a less level playing field, the match was on the kind of medium-speed hard court the Bryans like, before a home crowd.

While Marcelo Melo and Bruno Soares have won “only” four doubles titles (no majors), discerning fans knew they have a hex on the Bryans. They led the head-to-head by 2-1 going into this one. In another three-and-a-half hour clash, the Brazilians prevailed, 7-6 (6), 6-7 (7), 6-4, 3-6, 6-3. John Isner, the U.S.’ top singles player, has shown that he’s capable of handling the unique pressure of Davis Cup (not all players of his class can), and he’ll have to show it in Sunday’s first singles, against the mercurial Brazilian No. 1, Thomaz Bellucci.  

Austria trails at Kazakhstan, 1-2: Austria has never been known as a tennis power, but Jurgen Melzer has been ranked as high as No. 8 in singles. He lost on Friday to Evgeny Korolev, who’s ranked 181 rungs below No. 30 Melzer. That was right after No. 107 Andreas Haider-Muarer of Austria was was upset by No. 187 Andrey Golubev.

The Austrians’ heads must have been spinning after the first day, but their doubles team of Alexander Peya and Julian Knowle upended Golubev and 33-year old Yuriy Schukin, 7-6 (5), 6-3, 7-6 (3). That cracks open the door for Austria—bear in mind that while the doubles was a straight-setter, it lasted nearly three hours. Golubev is sure to feel it in his legs against Melzer, who had today off. This one looks like it could go five, meaning all bets are off.  

Czech Republic leads at Switzerland, 2-1: Where is that danged Roger Federer when you really need him? Today, Tomas Berdych and Lukas Rosol of the Czech Republic won a seven-hour and one-minute marathon on Swiss soil against Stanislas Wawrinka and Marco Chiudinelli, 6-4, 5-7, 6-4, 6-7 (3), 24-22. It’s now officially the second longest match in tennis history, after that 70-68 in-the-fifth singles win at Wimbledon, Nicolas Mahut succumbing to Isner.

Give Berdych and Rosol props for hanging so tough on the Rebound Ace hard court in Geneva. While the Swiss are well-mannered fans, they make noise and carry on with the best of them. And give Wawrinka and Chiudinelli credit for fending off an incredible 12 match points in the fifth set before they capitulated. It isn’t often that doubles makes it into the headlines, but rest assured that this match will be acknowledged far and wide, especially in Switzerland and the Czech Republic.  
You can’t ask for a better example of the critical role doubles plays in Davis Cup. The Czechs, crowned Davis Cup champions of 2012 just two months ago on home soil, are in a pretty good position to enjoy their reign for at least a few more months. Both No. 1 players (Wawrinka and Berdych) were involved in today’s match, so it will be interesting to see which one of them sucks it up and wins the first rubber tomorrow.  
Should Wawrinka rally and come through, 20-year old Henri Laaksonen will have his work cut out (if he plays the second singles, as planned). He’s ranked 200-plus places below No. 73 Rosol, and played his first-ever World Group match on Friday.  
As all eventful doubles days must, this one has set the table for a compelling Sunday.