Jon Heyman of FanRag Sports earlier reported the two sides were close to an agreement.
There were rumblings prior to the start of the 2016 season about Arrieta seeking a deal up to seven years, though Nightengale noted when the Chicago Cubs met with the right-hander, they didn't want to exceed five years.
While Arrieta was still terrific in 2016, his performance wasn't as impressive as his Cy Young campaign in 2015.
He posted a 3.10 ERA with 190 strikeouts in 197.1 innings, but his control abandoned him at times. He led the league with 16 wild pitches, and his walk rate nearly doubled from 1.9 per nine innings in 2015 to 3.5, per Baseball-Reference.com.
After a slow start in 2017, Arrieta looked more like the pitcher who won the Cy Young two years ago. The then-31-year-old posted a 2.28 ERA with 61 strikeouts in 67 innings pitched after the All-Star break.
Despite those early struggles, Arrieta wasn't concerned about receiving what he believed would be a fair-market value for his talent in the offseason.
"You can struggle for a little while," he told Nightengale in August. "It's going to happen. If a guy hits .200 for a while, it doesn't mean he's a .200 hitter. Everyone wants to have a career year, but if I stick to what I'm doing, I like my chances. I'll be fine."
There's always a significant risk investing big money over many years to starting pitchers, especially one like Arrieta who only has two seasons in his career with more than 170 innings pitched.
The Phillies are betting big on Arrieta maintaining his 2017 second-half form.
Arrieta has shown his ability to dominate an opposing lineup at his best over the past four seasons with the Cubs, including a 3.63 ERA with 25 strikeouts in 22.1 innings during the 2016 postseason to help the franchise win its first World Series in 108 years.
The Phillies were a surprise suitor for Arrieta, though his addition makes all the sense for the current state of this team. Their financial situation was among the best in MLB this offseason with only two players under guaranteed contracts, not including those eligible for arbitration.
Those limited financial commitments give the Phillies' front office an opportunity to make a big splash in free agency to expedite their rebuilding process.
Adding Arrieta to the rotation along with Aaron Nola, who posted a 3.54 ERA with 184 strikeouts in 168 innings, gives the Phillies an excellent duo to build around.
Coming off three straight seasons with at least 90 losses, the Phillies had to take drastic action. They swung for the fences by pursuing Arrieta, arguably the best free-agent starter on the market, and wound up hitting a home run by signing him.
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