SYDNEY — The sudden departure of Nine topper David Gyngell earlier this month has sparked a game of musical chairs at rival terrestrial web Ten, with execs grabbing a seat lest they find Gyngell sitting in it.

The long-touted retirement of CEO John McAlpine after 30 years with Ten appears to have been fast-tracked, clearing the way for sales topper Grant Blackley to take the job July 1.

Blackley, who has worked for Ten for 18 years, will be replaced by his deputy Shaun James.

McAlpine has been credited with much of Ten’s success in the younger demographic, with its reality skein juggernauts “Big Brother” and “Australian Idol,” now in their fifth and third outings, respectively. It is a strategy that has seen Ten remain third in the ratings — behind Nine and Seven — but often first in profitability.

“While I will miss being in the thick of it, and numerous colleagues and friendships forged over many years, it’s time for some fresh blood at Ten’s helm and fresh air for me,” McAlpine says.

Speculation has been rife that Gyngell was in line to usurp Blackley, so it is believed Ten sped up McAlpine’s departure to stem any harmful gossip. But the move strikes Blackley off the list of potential successors to Gyngell — another source of industry chitchat.

McAlpine’s name also has been linked to the top job at Nine, but Ten’s exec chairman Nick Falloon says he will stay linked to the network “via a long-term consultancy agreement.”

McAlpine has also said he has no desire to work for another net.

So Gyngell’s future remains uncertain, and he is not commenting on where he might end up, preferring to shun the limelight in favor of time to reflect — and surf.

The exec threw in the towel at Nine, the flagship terrestrial channel of Kerry Packer’s Publishing and Broadcasting, after learning that TV vet Sam Chisholm was on his way back as exec director of television interests.

Chisholm is not wasting time shoring up his network in the face of a ratings challenge from Seven, which has had huge success this year beating out Nine, whose motto “Still the One” is looking shaky.

This week Chisholm poached Seven’s deputy news director Tony Ritchie, who has been instrumental in lifting the ratings of Seven’s news and current affairs skeins.

Which means it is likely there will be more reshuffles in the Oz network boardrooms before the music stops.