Newsday Publisher Tim Knight abruptly quit yesterday, ending a tumultuous five-year reign during which he survived the aftermath of a circulation scandal, a walkout by top editors and the paper’s sale to Cablevision.

The news of Knight’s resignation caught many within Newsday by surprise.

“Nobody had any heads-up,” said an insider.

In a note to the staff, Knight said, “Now is the right time to let others move our business forward. I have decided to resign as publisher.”

Knight is being replaced by Terry Jimenez, who will serve as acting publisher. Jimenez was most recently the publisher of amNew York, a freebie paper owned by Newsday and distributed in New York City, and previously served as Newsday’s CFO.

When he first arrived five years ago, dispatched from Chicago by then-parent Tribune Co., Knight was hailed as a savior at a time the paper was being rocked by a circulation-pumping scandal that prompted a federal investigation.

Yet circulation issues would continue to dog the paper after Knight engineered a retreat from the paper’s once ambitious strategy of covering New York City. In March, daily circulation was 368,194, vs. 482,182 five years earlier.

He also made successive rounds of cuts on the editorial side of the paper.

But perhaps the hardest part of his job came in January, when he worked behind the scenes to save the job of Editor-in-Chief John Mancini, who had been ordered out by Cablevision brass after the paper covered a story about sexual harassment claims against Knicks center Eddy Curry by featuring it on both the front and back covers.

Cablevision in the summer of 2008 had bought Newsday from billionaire Sam Zell, who had purchased Tribune in late 2007. Cablevision also owns the Knicks.

Sources said Newsday’s coverage of the Curry affair left Cablevision execs fuming, and Knight played a key role in quelling the unrest and convincing Cablevision brass to keep Mancini, who, along with his two top lieutenants, had walked out of the office for three days.

But while Knight’s maneuvering endeared him to some in the newsroom, not all were sold.

“When he first came here, I thought he was a breath of fresh air, but then he started cutting and trying to dismantle the paper,” said Michael O’Connor, president of the 1,100-member Graphic Communications Conference of the Teamsters, which includes all the paper’s unionized employees.

Six months ago, union members started handing out flyers in the Newsday parking lot that were critical of Knight’s management.

Knight oversaw the paper’s redesign of its Web site in July, which experienced a drop in unique visitors after it was unveiled. But Knight cited the relaunch of Newsday.com as one of his accomplishments. keith.kelly@nypost.com