The member of the 2006-07 "We Believe" Warriors made his debut a couple days later, and immediately became a part of the rotation.
Although he ended up not playing much in the postseason because of KD's return to the lineup and his own ankle sprain, Barnes earned that NBA championship ring.
And perhaps more importantly, he experienced some unbelievable moments that he never will forget. One such memory was created on March 29, 2017 just hours before Golden State faced off against the San Antonio Spurs.
Warriors coach Steve Kerr told the awesome story on the most recent episode of Barnes' "All the Smoke" podcast:
"It's one of my favorite NBA stories from coaching. One of the things I believe in as a coach is involving family members in any way that you can. It's really fun.
"So we always invite guys to bring their kids, their families, on the plane if you want. So we had a game in San Antonio. We have a breakfast meeting, and you bring your boys -- the twins. Everybody's having breakfast and then we're gonna get the meeting started.
"You were like, 'Coach, should I send the kids back?' I was like, 'Nah, nah, they're good.' And they're hoopers. They'd shoot around before practice. They love this stuff.
"It was Mike Brown's scout, so I said, 'Mike, why don't you go through the matchups.' He goes, 'All right, we're gonna change the starting lineup ... tonight we're gonna start Steph (Curry), Klay (Thompson), Matt -- you're gonna start at the three and you're gonna guard Kawhi (Leonard).'
"And your boys get up (from their seats) and they start pumping their fists, they're like, 'Yeah! Yeah (laughter)!' It was one of my all-time favorite moments because that's ultimately what it's about.
"How cool was that? There were your boys watching this team meeting and, 'Hell yeah, dad is starting tonight.' "
That. Is. So. Awesome.
"The kids' ride was the best time," Barnes said. "You couldn't tell these guys they weren't on the Warriors. You couldn't tell the twins they weren't a part of that team. These kids were on cloud nine.
"I thanked you, but I never got a chance to really thank you. That was a perfect exclamation. My kids got to see me play (and) they got to be a part of this special team. It was a perfect time to say goodbye (retire).
"And I really owe a lot of that to you and the Warriors organization for accepting me back. So thank you very much for that coach. I really appreciate that."
I'm not crying. You're crying.
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Just to refresh your memory -- the Warriors entered the game that night with a 60-14 record, while the Spurs were 57-16. It was a very important showdown.
Golden State fell behind 15-0 and trailed by as many as 22 points in the first quarter. But the Dubs ended up winning 110-98.
Barnes went 1-for-2 from 3-point territory and registered five rebounds and four assists in 26 minutes.
Thanks for sharing that story, Mr. Kerr.