Lara Flynn Boyle is back with Jack!

Pals of the pencil-thin star of “The Practice” say that the on-again, off-again relationship between Boyle, 32, and Jack Nicholson, 65, is definitely back on track . . . and that things started getting serious after they attended a baseball game between the New York Yankees and the Anaheim Angels in early October.

“Up until then, it seemed as if the chances of Lara and Jack getting back together again were about as remote as the Angels winning the World Series,” said a source close to the couple. “But now look what’s happened.

“Lara and Jack are in love again . . . and the Angels are baseball’s World Champs!”

When Jack performed at an all-star charity play reading on November 4, Lara was there for her man, offering her support.

“Jack was jumpy before the event because he’s not used to doing theater — even though this was just a reading,” said an insider. “Having Lara there soothed him and calmed him. She was his biggest cheerleader.

“Afterward, everyone asked the two of them if they were back together, but they coyly refused to confirm that they were. But it was clear that they were a couple — they held hands and had their arms around each other — and when they thought no one was looking, they even stole a few kisses!”

After Lara and Jack broke up in early 2002, the actress played the field — seeing first handsome young “Gideon’s Crossing” actor Eric Dane, and then Harry Morton, the 21-year-old son of Las Vegas Hard Rock Hotel owner Peter Morton.

But both romances burned out in a matter of weeks, and friends say Lara never forgot Jack.

“Jack has always been the great love of her life,” said one pal, “and he probably always will be. Even when she wasn’t with him, he was still very much on her mind. She desperately tried to make him jealous.

“When she was in London for a screening of ‘Men in Black II’ in July, she wore a jacket with a message handwritten on the back that said, ‘I’M HAPPY IN SPITE OF YOU.’ But the truth was that Lara really wasn’t happy at all without Jack.”

But now, she’s ecstatic.

“This time, Lara truly believes their love will last,” said the source.