In the split second that his mother let go of his hand, 22-month-old Stuart Tito scampered onto a subway train as it pulled away.

"I looked down, he wasn't there," Blanca Amarilis told the Daily News in Wednesday editions. "I said, 'Stuart!' and a man told me he went on the train. It was so fast. I was so upset."

"I thought that someone would take him," she said. "I prayed to God to protect my son and let me find him again."

A mysterious Samaritan did come to the rescue — returning 22-month-old Stuart to his panicked family, then vanishing.

Stuart, his parents and baby brother were on the Junction Boulevard platform in Queens on Tuesday when the events unfolded.

Amarilis, 33, had been holding Stuart's hand tightly: He's a restless bundle fascinated with trains. But she let her guard down for a split second while wiping baby Derrick's runny nose.

That was enough time for Stuart's little legs to carry him onto the Manhattan-bound No. 7 just as the doors slammed shut and it pulled away.

A woman on the train saw it happen. She scooped up Stuart, got off at the next station — 61st Street in Manhattan — and then took another train back to Junction Boulevard, where she spotted Stuart's anxious-looking father, Victor Tito, 32.

"Is this your son?" she asked.

"Yes!" he responded, enveloping his son in a hug.

Before he could even thank her, she disappeared into the crowd.

Stuart's mom, meanwhile, had hopped onto the next Manhattan-bound train with Derrick. Her husband called her with the good news.

"It was about 15 minutes — but it felt like forever," said Amarilis.

It seems, by the way, that Stuart has yet to learn his lesson.

As the family returned to the same station later in the day, he tried to make another dash for a No. 7 train as it roared in.

This time, his mom's grip remained firm.