Like he had done eight times before, Andy Roddick sealed a victory for the American Davis Cup team over the weekend — and like so many times before, twins Bob and Mike Bryan were the reasons Roddick had something to clinch.

When the American team returns to the Davis Cup final for the first time since 2004, Roddick will be the team’s best player. But the Bryans will lead the way. In all of the Davis Cup — considering every team and every man, even the occasional ones such as Roger Federer — they are the most important teammates in tennis.

The 29-year-old twins from California are now 12–1 in Davis Cup matches, two wins away from tying John McEnroe and Peter Fleming (14–1) as the best doubles pairing in the team’s history. When so much can go wrong in singles — injuries, exhaustion, and difficult surfaces — they are essentially a lock to win a point, no matter the city or surface. No other team in tennis has that. The Americans haven’t had it since McEnroe and Fleming retired (and, incidentally, that pairing’s one loss came in Sweden to the team of Stefan Edberg and Anders Jarryd, in 1984, perhaps the most embarrassing loss in the history of the American Davis Cup).

The twins were not facing Edberg and Jarryd over the weekend, but a team perhaps almost as formidable: Jonas Bjorkman, one of the best doubles players in the history of the game, and Simon Aspelin, who partnered with Julian Knowle to win the U.S. Open earlier this month (beating the Bryans along the way). There was no upset this time, as the Bryans turned this difficult contest into a demonstration of their superior skills, 7–6(11), 6–2, 6–3.

The first set tiebreaker featured fine shot making and sportsmanship. The twins led 2–1 when it appeared that Bob hit a reflex volley to steal a point off of Bjorkman’s serve. The chair umpire called the score 3–1, but Bob admitted that the ball had bounced off his body, not his racket. That made the score 2–2, and the two teams had played to 9–9 when Bob hit an ace for a 10–9 lead. He then successfully blocked an overhead aimed at his stomach, but Bjorkman recovered to win that point, as well as the next one on the most acrobatic shot of the match, a running, crosscourt overhead from nearly outside the right doubles alley.

Bjorkman’s magic gave the Swedes set point. But Mike saved the Americans with what his brother called the best volley of their season, a backhand half volley crosscourt off a quick bounce. Bjorkman couldn’t handle it, and the twins won the next two points, finishing the set on a great forehand return (from Mike) that forced Aspelin to volley into the net.

The twins played flawlessly the rest of the way, giving the American squad a 2–1 lead heading into Sunday’s reverse singles matches, and taking the pressure off James Blake, who continues to struggle in Davis Cup matches. The American looked listless in a loss to Thomas Johansson on Friday, a defeat that dropped his Davis Cup record to 11–8.

An American team has not won the Davis Cup since 1995, the longest drought in its history. The team’s last trip to the finals came in 2004, when they lost 3–2 on the road to Spain on clay. This time, the Americans will choose the city and surface against Russia, who rallied from a 2-1 deficit to defeat Germany over the weekend. The Russians beat the Americans in last year’s semifinals 3–2 on clay in Moscow before winning the Davis Cup against Argentina. It would seem strange for American fans to root for Russia, the deepest team in the field, against Germany, a surprise semifinalist with a limited roster. But the most dangerous opponent for the American squad is clay, not any one team. Against Russia, they’ll control their own destiny on a fast hard court.

The Bryans are the biggest reason why they’ll be tough to beat.

Casual tennis fans tend to look at doubles as a sport for also-rans, and generally assume that two better singles players would defeat the best doubles teams if given a fair amount of time to practice together. This is nonsense, and Wayne Bryan, the father and drill sergeant of the twins, is always more than happy to explain why. The Bryans’ success derives not just from knowing each other well and understanding set plays, but from the way they train. They work on volleys from deep in the court, they emphasize quickness, and they hit a lot of balls right at each other — hard.

What keeps the Bryans from being great singles players is their lack of speed around the court (speed is less essential in doubles since there are two players), and strokes that do not hold up in long rallies, which rarely happen in doubles (such rallies are rare in doubles). But when it comes to serves, volleys, and reflexes when returning serve, they are among the best tennis players in the world. When Russia comes to town at the end of November, they’ll already be down 1–0. That’s a tough way to start a tie on the road. The Bryans have won all four majors as a team, but never the Davis Cup. This year ought to be their first.

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While the Americans and the Russians have been full-fledged superpowers in the Davis Cup the last few years, parity has hit the rest of the field like never before. Consider that Switzerland, home of perhaps the best player in the game’s history, did not qualify for the World Group at the beginning of next year (Federer’s loss in doubles to the Czech Republic proved the difference). Neither did the once formidable Australians (Serbia knocked them out).

But for the first time in 14 years, Israel did, thanks to the exceptional play of Dudi Sela, who scored two singles victories against Chile in a 3–2 victory in Israel. On Sunday, Sela charged back from two sets-to-one down to defeat heavy favorite Fernando Gonzalez, the no. 6 player in the world, 4–6, 7–6(5), 5–7, 7–6(7), 6–3 in five hours.

Mr. Perrotta is a senior editor at Tennis magazine. He can be reached at tperrotta@nysun.com.