So … is it the Nets or the Raptors?

After witnessing the Nets’ leisurely stroll through Games 3 and 4 this weekend, resulting in a pair of blowout wins to give them a commanding 3–1 series lead in their first-round series against Toronto, I’m still not sure.

But heading into tonight’s potential clincher in their Game 5 in Toronto, this is the right question for Nets fans to start asking. After all, they’ve made the Atlantic Division champions seem totally clueless at both ends of the court, to the point that tonight’s game almost seems like a formality.

Moreover, it’s an important question as we look ahead to a potential second-round series against Cleveland. If it’s really the result of an improved Nets team, then the series against the Cavs looks eminently winnable. On the other hand, if the series is mainly the result of the Raptors’ failures, then New Jersey faces an uphill battle against the LeBrons next week. It’s hard for me to divine whether it’s the Nets raising their game for the first time in memory, the Raptors stumbling at the end of a surprisingly strong season, or perhaps some of both. Instead, all I can do is comb through the evidence and show you the facts that support each side of the case:

It’s the Nets, because of Richard Jefferson. Remember how I said that RJ held the key to this series? Well, he’s averaging 20.4 points a game so far, and with each passing contest we’re seeing a little more of the explosiveness in the transition game that was missing from him for much of this season.

A close-to-full-strength Jefferson combines with Jason Kidd and Vince Carter to give the Nets the perimeter scoring trio that gave opponents so much trouble a year ago. It also takes the heat off Jason Kidd to be a scorer and lets him focus on his brilliant passing, something that was on full display in the two wins this weekend.

It’s the Raptors because of injures. It should be pointed out that this Raptors team isn’t at full strength right now. Ever since starting small forward Jorge Garbajosa went out with a dislocated ankle — rivaling Shaun Livingston for the year’s most gruesome injury, if you missed it — the Raptors haven’t been the same defensively.

Garbajosa, a European vet who came over to the NBA this season, was his team’s Jason Collins. Though a floor-bound defender, he made up for his physical limitations at that end with toughness and smarts. And unlike Collins, he could make a basket once in a while and stretched defenses with his 3-point shooting.

Losing the Spaniard hurts even more because another foreign import, Andrea Bargnani, went out of the lineup at the same time. Bargnani came back just before the playoffs but has been horribly out of sync in the first four games, looking nothing like the player who was running a close second to Portland’s Brandon Roy in the Rookie of the Year chase pre-injury. For the Nets’ sake, they better hope his timing doesn’t came back this week, because he’s the one guy whose emergence could get the Raptors back into this series.

It’s the Nets because of the defense. The Nets’ identity throughout the Jason Kidd era has been as a defensive team, but that passion has been missing for much of this season. New Jersey ranked only 14th among the league’s 30 teams in Defensive Efficiency (my measure of a team’s points allowed per 100 possessions) for the season, a far cry from their third-place showing a year earlier. Part of that is a result of Jefferson’s decreased mobility, but other factors — a less athletic bench and Kidd’s age, for instance — also played roles.

But against Toronto, New Jersey has appeared notably sharper. Collins has done a much better job on Chris Bosh than I would have expected, taking away his driving lanes and forcing him to shoot jumpers over his outstretched hands. It helps that the Nets are running extra defenders at him too, with Kidd the most prominent helper. And despite Kidd’s vulnerability to the quickness of the Raptor guards, his ability to pester a post player and still recover to his man is second to none. That makes the jobs of Collins and Mikki Moore abundantly easier.

It’s the Raptors because of their role players. Or maybe I should say their former role players. What’s happened to Juan Dixon and Joey Graham in this series is beyond puzzling. The two wing players played a huge role in Toronto’s season-ending push to win the Atlantic Division, especially after Garbajosa and Bargnani went down.

But once the post-season started, they imploded. Graham finished his regular season with six straight double-figure efforts, but has scored a grand total of 12 points in four playoff games. Dixon only has him beat by three, and he got much of that well after the outcome of Game 4 had been decided. At 6-3, 164 pounds, Raptors coach Sam Mitchell has also had difficulty finding spots to play him, as Dixon is far too small to defend Carter or Jefferson.

The struggles of those two have forced Mitchell to turn to Morris Peterson (3.8 points per game in 23 minutes of inaction) or even Luke Jackson (!) in a desperate effort to find offense off the bench. And with Toronto only getting production from three of the five positions, it’s made defending the rest of the Raptors easier.

It’s the Nets because of the 3-point shooting. New Jersey has been beating the Raptors with the longball, especially on Sunday when they made 10 triples before halftime. For the series, New Jersey is making nine a game and hitting 37.1% from downtown. Heck, even in the one game they lost, they had a wide-open 3-pointer to tie it that just missed for Boki Nachbar.

For the series, Nachbar (50%), Carter (40.9%), and Kidd (42.9%) all have been devastating, and this isn’t low-volume shooting — they’ve collectively attempted 70 longballs in the series and converted 33. If the Nets keep shooting like that, the Raptors will be eliminated regardless of whether they solve their other problems.

jhollinger@nysun.com