There’s an exception to every rule, and tonight we may see two exceptions to the same rule back-to-back. The well-known rule in this case is the one that says the home team always wins Game 7 in the NBA playoffs. In the league’s history, road teams only have an 18.1% success rate, including Cleveland’s defeat yesterday in Detroit. Thus, when the Mavericks visit San Antonio tonight, and the Clippers venture into Phoenix, one would expect both teams to fall short.

However, that historical trend doesn’t include another important piece of information about those series. Historically, the reason the home teams did so well in those seventh games is because, by and large, they were the better team. Having earned home court by sporting a better record in the regular season, most of them were pushed to a seventh game by fluky outcomes in the first six contests – such as Cleveland’s three narrow wins over Detroit last week.

Thus, to make a case that Dallas or L.A. can buck the trend, we must either demonstrate that these teams are fundamentally better than they were in the regular season, or that their opponents are fundamentally worse. Surprisingly, there’s a fairly large body of evidence to support each proposition.

Both L.A. and Dallas have one major reason explaining why they’re better than they were during the regular season, and an equally important reason their opponent is worse. The scoreboard backs me up on this. Through the first six games of their series, both the Clippers and Mavericks outscored their higher seeded opponents by sizable margins (+20 in Dallas’s case, +27 in L.A.’s). Based on those victory margins, the Spurs and Suns should consider themselves lucky there’s even a Game 7 to be played.

We have little reason to expect things to change tonight. Let’s take a closer look at the reasons why Mavs and Clippers fans should be celebrating tomorrow:

Devin Harris and Keith Van Horn are playing. Harris missed 26 regular season games and was massively underutilized by Dallas in most of the others, with head coach Avery Johnson reluctant to expand his role beyond playing token minutes as Jason Terry’s backup. But when the series against San Antonio started, Johnson finally realized that Harris was one of his best players and threw him into the starting lineup.

The move turbo-charged the Mavs’ offense thanks to Harris’s ability to beat his man off the dribble. And really, it was long overdue. Harris ranked eighth on the team in minutes, but he was the Mavs’ fourth-best player based on my Player Efficiency Rating (PER, my rating of a player’s per-minute statistical production). Replacing offensive nonentity Adrian Griffin with Harris makes the Mavs a much better team than they were in the regular season.

On a less dramatic scale, the return of Van Horn does the same thing. The ex-Net missed 29 games, including all but five after February 25, and like Harris tended to play sparingly when he did see action. His presence gives Dallas a full complement of healthy players – a rarity at this point in the season. It also allows the Mavs to play Van Horn and Dirk Nowitzki in the same frontcourt, which gives opposing big men fits trying to match up with two big men hanging out at the 3-point line.

San Antonio has to play a different game against Dallas. Despite being the league’s best defensive team in the regular season, the Spurs had huge problems defensively in the first four games of the series because Dallas essentially broke their system. San Antonio’s defensive schemes depend in part on having two big men to protect the basket, but the Spurs can’t line up that way against Dallas because the Mavs’ small lineup will run circles around them. As a result, big men Rasho Nesterovic and Nazr Mohammed have become expensive pieces of furniture at the end of the bench, and playoff ace Robert Horry has been relegated to a lesser role as well.

Added to that is San Antonio’s baffling insistence on keeping Nick Van Exel in the rotation ahead of Beno Udrih. Though easily the Spurs’ worst regular, Van Exel’s status as a playoff hardened vet has earned him the trust of head coach Gregg Popovich, a trust which remains intact regardless of how badly Van Exel plays. Thus far in the series, he’s spent 61 minutes scoring a pal try eight points and getting beaten defensively. By playing him at the expense of Udrih and keeping their centers on the sidelines, the Spurs are a lower quality team than the one we saw in the regular season.

Corey Maggette is back. Maggette only played in 32 games this year due to a variety of injuries. The Clippers had a 47-win season in his absence and discovered a defensive stopper who plays the same position in Quinton Ross, so when the playoffs began, L.A. didn’t seem to have much of a role for Maggette.

But now that he’s healthy and the Clips have their backs to the wall, Maggette’s advantages are too obvious to ignore. The 6-foot-6 forward combines an accurate outside jumper with an electric first step on his way to the rim, providing a new dimension for a Clipper offense that was mediocre in the regular season.

Maggette also benefits from the heavy use of small ball in this series. When the Clips take out seven-foot Chris Kaman and insert Maggette as their “power” forward, he effortlessly blows by Phoenix forwards Boris Diaw and Tim Thomas. In Game 6, for instance, he scored 25 points in 27 minutes – while missing only one shot! In short, he’s become the X-factor that turned the Clippers from a decent regular-season club into a dangerous playoff team.

Steve Nash isn’t right. Nash might not have been the rightful MVP, but he’s way better than this. His numbers in the L.A. series are so far short of his career norms, and his defensive shortcomings have been made so apparent, that it’s clear his back and leg problems are affecting him much more than he’s let on.

Nash is one of the four or five best shooters in basketball, but he hasn’t played like it against L.A. At one point he missed 14 straight 3-pointers, and he is only 6-for-28 overall. Almost all of them were wide open, and nearly all bounced limply off the front rim, suggesting his legs aren’t generating the power they should. Meanwhile, the Clippers are attacking him at every opportunity – even with a defensive specialist like Ross, who shattered his career-high by scoring 18 on Nash in Game 6.

While Nash refuses to make excuses, it’s easy to see how the postseason wear-and-tear could be bringing him down. The Suns played a seven-game first round series and have had almost no rest since the playoffs began. The one ray of hop is that Nash takes the court tonight with three days of rest, which could help him rediscover the form that so captivated the league in the regular season.

Mr. Hollinger is the author of the 2005-06 Pro Basketball Forecast.