Superman jinx? What Superman jinx?

After previous television incarnations of the Man of Steel lasted no more than four seasons, the WB’s “Smallville” has surpassed them by not only surviving to a fifth season, but thriving in it.

Shifted to a tough Thursday night slot, the story of young Superman has defied conventional TV wisdom by having its best season to date in key ratings categories.

No longer opposing ABC’s hot drama “Lost” on Wednesday, “Smallville” is averaging 5.5 million viewers this season, up 8% from a year ago. It’s also set Thursday records for the WB.

“It’s not surprising that ‘Smallville’ has a loyal core audience who would follow it to a new time period,” says media buyer John Rash of Campbell Mithun, “but it did it in the teeth of tough Thursday competition and the more-hyped premiere of ‘Everybody Hates Chris’ on UPN.

“It consistently delivers its desired demo, only now on a crucial marketing night.”

WB entertainment prexy David Janollari, looking to spread his rebuilding net’s assets across the sked, says the decision was made because there was an opening for young viewers on the night — and Thursday “isn’t what it used to be competitionwise” now that “Friends” is gone.

“It was one of those moments of looking at the board and saying, ‘Hmmm, what about this?’ ” he says. “The sales group lit up and said, ‘Yeah, we can do business there.’ ”

Thursday is the most lucrative night from an advertising perspective, in large part because film studios pay top dollar in a bid to attract young adults to their pics on the weekend. And in “Smallville,” the Frog has its first real significant presence there.

Peter Roth, president of Warner Bros. Television, producer of the series, says the timeslot move was risky but has clearly worked.

“Give credit to the network, because the competition is less formidable and they found a good spot for it,” he says. “This is arguably one of the biggest hits we’ve produced as a show for our sister company.

“It’s a wholly owned Time Warner property, and it’s been given the full weight and impact of the network, which has made for a happy association.”

Series creators Al Gough and Miles Millar, whose film work includes “Shanghai Noon” and “Lethal Weapon 4,” credit Roth and a moment of “serendipity” nearly six years ago that led to the creation of the series.

The writing partners had a relationship with WBTV since 1999, and in the summer of 2000 they pitched a series about Lois Lane, whom they envisioned as a cross between Ally McBeal and Nancy Drew.

“We thought we could never get the rights (to Superman), so we went in a different direction,” Gough recalls. “But at the same time, Peter was trying to secure TV rights to Superman.”

Gough and Millar were then off and running, creating their own “Smallville” mythology while trying to stay true to Superman characters in the DC Comics.

“Batman had always been considered cool and Superman kind of cheesy, so we wanted to ground Superman in reality,” Gough says.

They literally grounded him, too, setting up a “no tights/no flights” rule at the outset to make a young Clark Kent more relatable to auds.

“Superman’s always been malleable to the times, from the ’50s to the ’90s when he was a yuppie, so we went the angst-ridden teen route,” Gough says. “He’s a contemporary teen that just happens to be from a different planet.”

Among the chances taken by the creators were the addition of Chloe as a confidante to Clark, and beefing up the character of Lionel Luthor, father of Lex.

“Lionel wasn’t intended to be a long-term player, but he affects Lex so much and we were so intrigued by the parallel of extreme parenting,” Gough says. “Why does Clark Kent become Superman and Lex who he is? It’s really how they are raised.”

Looking forward, this fifth season is a key one in the Superman mythology. Clark and his friends are in college and the working world in Metropolis, and he is discovering more of his powers as he becomes involved deeper with his legacy as a son of Krypton.

“This is where Clark starts to step up and take the mantle of Superman,” Gough says, “and Lex’s descent into evil is accelerated.

“And now that everybody’s legal, we can play that Clark-Lana-Lex triangle and see that effect.”

Show has been successful for ABC Family in syndication and is doing very well overseas, where it has become Warner Bros. Intl. Television’s highest-rated and most well-received series since “ER.”

A sixth season is expected, but nobody involved with the show will commit beyond that at this point.

“Advertisers love ‘Smallville,’ and it’s been wildly successful for our network in terms of revenue,” says Janollari, adding that it has helped expand the WB’s audience by bringing in young males.

“For as long as it’s around, its popularity can help us rebuild and find that next wave of hits.”