After a close season of unprecedented upheaval in the English Premier League, the 2013-14 campaign, starting on Saturday, looks set to be the most tightly-contested in recent memory.

For the first time since November 1986, defending champions Manchester United have a new man in the dug-out, with former Everton coach David Moyes stepping in after the retirement of the legendary Alex Ferguson.

Manchester City, champions in 2012, also have a new manager in the form of Manuel Pellegrini, while the most headline-grabbing appointment of the summer saw Jose Mourinho sweep back into Chelsea after six years away.

In total, there have been five managerial changes, and with a new £5.5 billion ($8.5 billion, 6.4 billion euros) television rights deal kicking in, England's elite clubs have been splashing the cash as rarely before.

United romped home 11 points clear of City last season, but their aura has faded in the wake of Ferguson's abrupt exit, and Moyes faces a challenge to prove himself a worthy successor.

The champions' pre-season has been dogged by speculation about the future of striker Wayne Rooney, the subject of two failed bids from Chelsea, while the pursuit of Barcelona midfielder Cesc Fabregas came to nothing.

Moyes faces a taxing start, with games against Chelsea, Liverpool and City awaiting in the first six weeks of the season, and he is well aware of the threat to United's 20-year dominance amid the current state of flux.

"There are new managers coming into clubs, so things can change," Moyes told journalists on United's tour of Australia.

"I think the Premier League is going to be a little bit more unpredictable than it's been in the past.

"(Arsenal's) Arsene Wenger is now the longest serving manager in the league and there is the chance that this could be a different kind of year."

United have failed to make inroads in the transfer market, with 20-year-old Uruguayan right-back Guillermo Varela their only signing to date, but City, Chelsea and Tottenham Hotspur have all strengthened.

City have spent the most conspicuously, parting with around £90 million in a bid to close the gap on United, but they have recruited intelligently.

Alvaro Negredo and Stevan Jovetic will bolster an attack that has lost Carlos Tevez and Mario Balotelli in the past eight months, while Fernandinho and Jesus Navas bring power and pace to Pellegrini's midfield.

Spurs have also invested heavily, breaking their transfer record twice to sign Paulinho and then Roberto Soldado, but their fortunes may hang on whether or not they can resist Real Madrid's interest in last season's serial award-winner, Gareth Bale.

Arsenal pipped Spurs to a Champions League place last season, but despite Wenger threatening to flex his muscles in the transfer market for once, they missed out on striker Gonzalo Higuain and have been rebuffed by Liverpool in their attempts to sign the unsettled Luis Suarez.

Mourinho's return is likely to have a strongly galvanising effect at Chelsea, who were briefly transformed into England's leading side during his first stint at Stamford Bridge between 2004 and 2007.

The charismatic Portuguese returns slightly chastened after a difficult experience at Real Madrid, but he has promised to squeeze every ounce of talent out of the Europa League champions' squad.

"I am not the kind of guy who makes life easy for the great players," he told The Guardian newspaper in July.

"Don't get me wrong -- I still prefer the top players, the guys who win you matches and make the difference. But if they are 'great', they have to give more than the others."

Further down the table, even the division's more modest clubs have capitalised on the largesse of the new TV package to enhance their squads.

League Cup winners Swansea City broke their transfer record to sign Ivorian striker Wilfried Bony from Vitesse Arnhem for £12 million, while Southampton beat off competition from several leading clubs to make Kenyan midfielder Vincent Wanyama a £12.5 million acquisition from Celtic.

Cardiff City's promotion from the Championship means the English top flight will witness a south Wales derby for the first time, but bookmakers are backing Malky Mackay's side to go straight back down along with Hull City and Crystal Palace.

The forthcoming season will also see the Premier League become the first national championship to use goal-line technology, with Hawk-Eye systems having been installed at all 20 club grounds.

The prospect of next year's World Cup in Brazil, meanwhile, will serve as an extra source of motivation for players during what is likely to prove an engrossing campaign.