PITTSBURGH — Mike Tomlin isn’t ready to say the Pittsburgh Steelers are back. Not after watching his team sleepwalk through the second half against Jacksonville on Sunday.

“The big challenges lie ahead,” the Steelers coach said after a 17-13 win over the Jaguars. “We need to prepare for them.”

The Jaguars gave the defending AFC champions plenty to work on.

Jacksonville (1-5) dropped its fifth straight to match the franchise’s longest losing streak in a decade, but it was the Steelers (4-2) who were apologizing after an agonizing 30 minutes in which they nearly frittered away a commanding lead.

“If you get out to a 17-point lead and get comfortable, you take it off their throat,” Pittsburgh wide receiver Mike Wallace said. “We have to keep the same intensity the whole game. We started out with a lot of intensity and then we fell off a little bit.”

And Jacksonville nearly took advantage.

Rookie quarterback Blaine Gabbert led a methodical comeback that didn’t end until his desperation heave on the game’s final play bounced harmlessly to the ground in the back of the end zone.

“The biggest thing is that we gave ourselves a chance,” Gabbert said. “We had an opportunity to win the football game at the end and we had to capitalize on that opportunity.”

Gabbert completed 12 of 26 passes for 109 yards and a touchdown — and even though he remains winless as a starter, the Jaguars remain competitive and upbeat. In the sad-sack AFC South, Jacksonville remains just two games out of first place.

“I guess the growing theme around here is that we’re so close,” wide receiver Mike Thomas said. “We’re doing some good things, but we’re not doing enough to finish the deal.”

It would help if the Jaguars started better. Pittsburgh overwhelmed Jacksonville in the first half, outgaining the Jaguars 315-68. Yet all that dominance translated into just a two-touchdown lead.

Then the Steelers let off the gas and nearly ended up empty in more ways than one.

The offense managed just 70 yards after halftime and All-Pro safety Troy Polamalu sat out Pittsburgh’s final two defensive series after experiencing concussion-like symptoms after stuffing Jacksonville’s Maurice Jones-Drew on a critical third down.

Tomlin said Polamalu was held out as a precaution. The Steelers didn’t need him to hold off Jacksonville, though the road gets significantly tougher over the next few weeks. Pittsburgh travels to Arizona next Sunday then hosts New England and Baltimore in what will be the season’s next litmus test.

If the Steelers play the way they did in the first half against the Jaguars, they can make some noise. If they play the way they did in the second half, they’re in trouble.

“It’s frustrating because my expectations for this offense are high,” quarterback Ben Roethlisberger said.

Pittsburgh appeared to be living up to them for a half. Roethlisberger hit Mike Wallace for a 28-yard touchdown pass and Rashard Mendenhall ripped off a career-best 68-yard run and scored a touchdown a week after sitting out a victory over Tennessee with a hamstring injury.

Mendenhall finished with 146 yards on 23 carries, while Roethlisberger passed for 200 yards and a score. But after the break, Mendenhall needed 11 carries to get 33 yards and Roethlisberger completed just one pass.

That allowed the Jaguars, who came in last in the league in total offense and passing offense, and 31st in scoring, to hang around.

“We didn’t play the style of football that we like to play in the second half,” Tomlin said. “All that being said ... we made the necessary plays at the end.”

And Jacksonville didn’t — again.

The Jaguars haven’t lost five straight since 2001, when Gabbert was 12. He’s 22 now, and impatient. Jacksonville didn’t turn the ball over and Gabbert stood his ground behind a rebuilt offensive line and a Pittsburgh pass rush that sacked him five times. It was a step forward, just not in the win column.

“We just have to score more points and come out with a sense of urgency in the first half like we did in the second half,” Gabbert said.

The Steelers have the opposite problem. They’ve won four of five, but have shown only flashes of their usual form. They know it’s time to get going.

“We’re going to get better, but we’re not going to apologize for this win,” wide receiver Hines Ward said. “We won that game. That’s all that matters.”

Notes: Ward caught three passes for 47 yards to move past Michael Irvin and into 19th place on the yards receiving list. Ward now has 11,939 yards. ... New Jacksonville punter Nick Harris, signed last week, averaged 42.3 yards on seven punts. ... Scobee’s two field goals gave him field goals in 14 straight games, a team record. ... Pittsburgh G Doug Legursky left in the second quarter with a dislocated toe.