Porto remain favourites despite Villas-Boas exit
Porto won the treble before Villas-Boas joined Chelsea in June, lifting the Europa League and the Portuguese Cup and going undefeated in the domestic league, finishing 21 points ahead of second-placed Benfica and 36 in front of Sporting in third.
Perennial sellers in the transfer market, Porto have so far retained their key players including powerful Brazilian forward Hulk and prolific Colombian striker Radamel Falcao.
New coach Vitor Pereira also made a flying start, guiding the team to a 2-1 win over Vitoria Guimaraes in Sunday's Portuguese Super Cup.
"The greatest fun about being a football coach is living under pressure, the higher the difficulty level the more at ease I feel. I enjoy it," he said.
Questions remain, though, about how the inexperienced Pereira will handle the pressure of the Champions League and the tougher competition at home especially if they cannot prevent one of Europe's bigger clubs prising Falcao away.
Benfica coach Jorge Jesus has tried to fill some of the gaps evident last term, particularly at the back.
"This is the most balanced group I've managed in my three seasons here, the squad has a lot of variety," Jesus said.
Keeper Roberto, whose blunders cost Benfica several points last season, has been sold to Real Zaragoza and the team are expecting much from Brazilian shot-stopper Artur, a new signing from Braga, and Portugal international Eduardo.
Fabio Coentrao, the team's top performer last term, has left for Real Madrid. But the arrival of Spain's Joan Capdevila will bring experience and Argentine centre back Ezequiel Garay should stiffen the back four.
Belgian midfielder Axel Witsel and Spanish forward Nolito have made bright starts, shining as Benfica knocked out Turkey's Trabzonspor in Champions League qualifying.
The biggest overhaul has been at Sporting where the new board hired coach Domingos Paciencia on the strength of his exploits with unfancied Braga.
Sporting, who have not won the league since 2002, have signed more than 15 players and made room for them by releasing several underperformers.
But pre-season form has been mixed and question marks hang over a leaky defence and about whether the coach can succeed at a bigger club.
Europa League runners-up Braga have caused the "big three" problems in the last two seasons although they look as if they could struggle without Domingos and several key players.