At 3 p.m. on Monday, Zach Thornton called his father, Paul, to share the news that the New York Mets were promoting him to pitch in Wednesday’s game for his major-league debut.

Paul answered the phone from Shirley Ryan AbilityLab in Chicago, where he has spent the past month-plus relearning how to walk after a spinal surgery went wrong.

“I’m going,” Zach told his dad.

The video chat was brief. Words are hard when emotions are so strong. Quickly, Paul’s eyes welled up with tears.

“OK,” Paul said to his son, “so are we.”

Paul checked out of the hospital, which means he cannot go back. The rest of his rehab therapy is going to happen in Kansas, where he lives, as an outpatient. That is fine, he said, as long as he can see Zach fulfill his dream of playing in the big leagues. The 24-year-old left-hander will start against Washington on Wednesday at Nationals Park.

“It was go and be a dad and support a young man in Zach or take care of my health,” Paul said. “The doctors at Shirley Ryan assured me that my health was in good hands and that they felt as though I could do it. So it really made my decision very easy.”

After that memorable video chat, Paul and his wife, Julie, traveled to Chicago O’Hare International Airport to board a flight bound for Washington, D.C. He moved around the airport in a wheelchair. Once they arrive at Nationals Park, they expect to watch their son from Section 114. Paul plans on sitting in a wheelchair seat.

Paul cannot yet walk on his own. Every day, he is making progress. One of his most recent milestones happened earlier this week when he walked 466 feet with the help of a two-wheel walker.

Paul, a former track star, decided his condition was not going to stop him from seeing Zach make his debut.

So he checked out of Shirley Ryan on Tuesday, less than two months removed from being temporarily paralyzed from the waist down.

“To be honest, as a dad, I’m not going to miss this,” Paul said.

Zach said Tuesday that the first call he placed after the Mets informed him of his promotion was to his father. Paul has watched every outing. Paul believed in Zach as a pitcher when few others did.

“I pitch with a big heart for him,” Zach said.

People who know Zach best describe him as an underdog. He stands at 6 feet 3, but he used to be the smallest player on his Little League teams. As a junior in high school, he logged just two innings for the varsity squad. Upon graduating in 2020, he went undrafted.

It wasn’t until Zach attended Barton County Community College in Kansas that his baseball career started to take off. As a freshman, he produced a 2.63 ERA with 91 strikeouts in 78 2/3 innings. His father helped him get noticed, too.

Paul is a track and field coach for the University of Kansas. One of Paul’s good friends is a track and field coach at Grand Canyon University. The friend showed a video of Zach to a Grand Canyon University baseball coach. The Antelopes then started recruiting Zach.

The Mets drafted Zach out of GCU in the fifth round of the 2023 amateur draft. Throughout his time in the minor leagues, Zach has developed a reputation for being unafraid. The tall lefty throws strikes.

Zach has pitched just two games in Triple A. Over a dozen innings at that level, he allowed just three runs and three walks while racking up 13 strikeouts. In need of a starter after losing veteran Clay Holmes to the injured list, the Mets could’ve called up Jonah Tong or Jack Wenninger, prospects ranked higher than Zach. Instead, they picked Zach.

When prompted, Zach described himself as “an ultimate competitor.”

It runs in the family.

“I 100 percent got that from him,” Zach said, of course referencing his father.

Until recently, so much of Paul’s life revolved around running and a track. He joined Kansas in September 2018 after 10 years at Minnesota, coaching the men’s sprinters, hurdlers, jumpers and multi-event athletes. Before his coaching career, Paul was a star athlete at St. Olaf College, making the all-Minnesota Intercollegiate Athletic Conference three times.

In late winter, Paul experienced some numbness on his right side. On March 22, he and Julie went on a 1 1/2-mile walk. Toward the end, he kept dragging his foot. Two days later, Paul went to the doctor for an MRI. On April 2, he had surgery to remove a tumor from his spine.

But Paul’s spine, he said, began to bleed during the operation. He was losing feeling in his lower body. The surgeon, Paul explained, got as much of the tumor out as possible before needing to stop. Within a day or so, Paul was transferred to Shirley Ryan. With Julie, he has documented his journey on social media. In his first video from the facility, he cried while saying his goal was to walk again in time for the NCAA Track and Field Championships in mid-June.

“I’m in it for the battle,” Paul said in his first video.

Over the phone from the airport, the only time Paul’s voice wavered when discussing the last couple of months was when he talked about the support he has received from his daughter, Marissa; her husband, Jackson; and Julie and Zach.

Despite spending much of the past two months with Double-A Binghamton, Zach has seen his dad a couple of times recently. After Paul’s surgery, the Mets flew Zach out to see his father. When Paul moved to Shirley Ryan, they flew Zach out to Chicago.

“They’ve been nothing but awesome,” Paul said.

The Mets are noncommittal about how long Zach’s stay in the majors will last. A lot of it likely depends on how he performs.

Once he gets back to Kansas, Paul said he plans to “work all summer” in hopes of walking on his own again as soon as possible. He wants one of his next steps to be watching Zach pitch without needing a wheelchair.

“The next time I go and get a chance to watch Zach pitch,” Paul said, “I’ll be able to go in with just a walker.”