The new Euroleague has 24 members including some of European basketball's biggest names - Real Madrid, Barcelona, Olympiakos Piraeus, plus London Towers - but the 'official' Fiba backed Suproleague can count on some top teams too.
Panathinaikos and Maccabi Tel Aviv - winners and runners-up in last season's Final Four - have stayed on.
The split was caused by a row over television money after Fiba negotiated a deal with marketing group ISL Worldwide.
More money
Several clubs were unhappy wih the spoils from the deal, saying they already had agreements in place that would bring them in more.
The split forced Fiba to scale down its newly-named Suproleague from 24 to 20 teams, including some less than household names.
The Union of European Basketball Leagues (Uleb) duly made good on their threat to split from Fiba and announced plans for their new competition, which guarantees the clubs a pool of $35 million a year for each of the five seasons of its contract with Spanish telecommunications giant Telefonica.
"At a domestic and European level in most sports now, the clubs themselves are taking part in the way competitions are run," Barcelona spokesman Gustau Calvache explained.
"The structure of the Fiba competition was based on the past. With this new competition the clubs are generating income themselves. We have much more control."
Guaranteed places
Several of the biggest clubs, including Barcelona, are guaranteed a place in the competition for three years.
After that, it will be based on past performances and qualification from national leagues.
"We're going in new directions with the sport. The fact that London Towers are involved, for example is very important."
Implications for football
The success of the new venture could also have implications for Europe's top football clubs, who have themselves been tempted by a breakaway league backed by TV money.
Indeed Telefonica were in preliminary talks with some of Europe's biggest clubs last year.
The format of the new Euroleague will follow that of the NBA with play-offs from the quarter-finals onwards.
That guarantees more games - and more revenue - as the season reaches its climax.
Olympiakos, the 1997 winners, get the new competition underway as they visit eight-times European champions Real Madrid on Monday.
Fiba's Suproleague has also changed format - as well as its name - to cope with the split.
Instead of 24 teams in four groups of six there will be just two groups of 10, with eight going through from each.
The Final Four were due to take place in Vitoria, Spain, but since Tau Vitoria have opted for the new Uleb competition, a new venue will have to be found.
Despite losing some of its biggest names to Euroleague, Fiba remain bullish about their competition.
"The split has been bad for European basketball and we very much hope it's not definitive," a spokesperson said this week.
"But we have three of last season's final four participants in Suproleague next season so we are very confident about our competition."