Collins checked in with 10:28 to go in the second quarter and received a round of applause from the Staples Center crowd.
"Sometimes in life something happens and there's an opportunity," he said shortly before taking on the Los Angeles Lakers Sunday night. "I'm very thankful for this opportunity. That's why I work so hard, why I train the way I do so that when I do have an opportunity physically I'm not worried about my conditioning or cardio or anything along those lines."
"The decision to sign Jason was a basketball decision," Nets general manager Billy King said in a statement. "We needed to increase our depth inside, and with his experience and size, we felt he was the right choice for a 10-day contract."
The Nets tweeted out a picture of Collins signing his contract.
Collins will wear No. 98 for the Nets, but was unable to wear it Sunday because it was not available in time for the game against the Lakers, so he wore No. 46 instead.
Collins' choice of the No. 98 is in honor of Matthew Shepard, a University of Wyoming student who died in a notorious anti-gay hate crime in 1998. Collins has worn the jersey number with both the Celtics and Wizards.
The Nets moved quickly to make the historic signing of the 35-year-old free agent center to have another big body available against the Lakers. Brooklyn had been contemplating signing Collins for the past week and the need for Collins became greater after the Nets dealt rebounding specialist Reggie Evans to the Sacramento Kings last week.
"Jason told us that his goal was to earn another contract with an NBA team. Today, I want to commend him on achieving his goal. I know everyone in the NBA family is excited for him and proud that our league fosters an inclusive and respectful environment," NBA commissioner Adam Silver said in a statement.
ESPN.com reported that the Nets quietly auditioned Collins last week in Los Angeles, paving the way from him to rejoin the franchise with which he spent his first six-plus seasons in the league.
The Nets were in the running to land Glen Davis but Davis opted to sign with the Los Angeles Clippers and informed teams of his decision. Davis is set to officially become an unrestricted free agent Sunday at 5 p.m. ET if, as expected, he is not claimed off waivers by another team.
Collins hasn't played in an NBA game since April 2013 with the Washington Wizards. Collins, who has a house in the Los Angeles area, said it was "pretty easy" to get to downtown for the game. He's been working out on his own for months in the L.A. area after failing to earn an invite to training camp from any of the league's 30 teams in the wake of revealing his sexual orientation to Sports Illustrated in April of last year.
"Life is so much better for me. I don't have to hide who I am. Just be my normal self," Collins said. "The past 10 months have been incredible. A lot of really cool experiences, learning a lot, making new friends and hearing peoples' stories. Overall, it's been really positive."
The Nets are an organization filled with Collins supporters and experienced players less likely to be fazed by the likely media blitz that the signing will inevitably spark. Over the last couple of days, several Nets players have publicly voiced their support for signing Collins.
"Guys know what to expect from me," Collins said. "They're not like 'he's magically gonna have a 40-inch vertical and shoot 3s.' My game has been pretty consistent. I'm a defensive player first, and that's what I pride myself on. Now it's just a matter of getting comfortable with coverages and assignments."
Collins is reunited with Nets coach Jason Kidd, who played with the defensive-minded big man in New Jersey from 2001-08, making two trips together to the NBA Finals. Collins also played with Nets guard Joe Johnson for three seasons in Atlanta and spent half of the 2012-13 season in Boston alongside Paul Pierce and Kevin Garnett before being traded to the Wizards. Collins also is friends with injured Nets center Brook Lopez, who like Collins played alongside his twin brother at Stanford.
"Great competitor, plays team basketball, is for the team, great guy, great character," Garnett told reporters on Saturday morning about Collins.
Garnett also scoffed at the notion that Collins' orientation with the Nets would be any sort of issue with the team.
"I think it's important that anybody who has the capabilities and skill level [gets] a chance to [do] something he's great at," Garnett said. "I think it would be bias, and in a sense, racist, if you [were] to keep that opportunity from a person."
The Nets' signing of Collins comes not long after University of Missouri defensive end Michael Sam announced he is gay earlier this month in an ESPN "Outside The Lines" interview. Sam, though, can't make his official NFL debut until the fall. Los Angeles Galaxy midfielder Robbie Rogers became the first openly gay male athlete to play in a U.S. professional sports league when he made his Major League Soccer debut in May 2013, just three months after coming out. And John Amaechi, who spent five seasons in the NBA with Orlando, Utah and Cleveland, disclosed his sexuality three years after his playing career ended in a 2007 book entitled "Man In The Middle."
Sam reacted to Collins news on Twitter.
Rogers also tweeted about Collins.
Very excited to watch @jasoncollins34 tonight more importantly I am proud to call him my friend.- Robbie Rogers (@robbierogers) February 23, 2014
Athlete Ally, a non-profit group that works closely with the NBA and other professional sports leagues on LGBT inclusion, applauded the Nets' decision.
"Today, Jason Collins tore open the last remaining closet in America, and became the first openly gay player to be signed by a team in one of the big four sports. We are especially excited that Jason will be playing in Brooklyn, just like Jackie Robinson, and in a marriage equality state. This is a piece of history, an important point on the continuum toward justice and a moment to celebrate," Brian Ellner, a member of the Athlete Ally board of directors said in a statement.
Asked if Collins' signing marked a landmark day for the NBA, Lakers coach Mike D'Antoni said, "I think it's very positive. It's good and we'll get to the point where you'll ask me if he's a good addition or not because he can play or not. That's what we need to get to."
In an interview with ESPN's LZ Granderson in January, Collins said he has been training hard while waiting for an opportunity.
"I try to control what I can control and that's how hard I train right now," Collins said. "I know that I'm in great shape and that if I get an opportunity ... if an owner, coach, GM calls my agent ... I'll be ready to play."
Asked if being gay has harmed his ability to get a call, he said: "I have no idea. For me, again, it goes back to what I can control, and that's my training."
Asked what has changed for him since he came out, Collins said: "I get to be who I am. I don't have to walk around with a censor button. I don't have to walk around with 'don't say this, don't do this.' "
Clippers coach Doc Rivers, who coached Collins in Boston, said Sunday he was happy to see the veteran center return to the NBA.
"We've been talking the last three or four days. Jason and I have texted and talked on the phone," Rivers said. "I'm very happy for him, just really for the basketball part. The other stuff is for everything else but just the basketball part. He's a worker, he's a good guy and it's always nice having good guys in the league. And it's a perfect place with Kevin [Garnett] and Paul [Pierce]. He was with us in Boston so they know what he can do defensively."
Collins doesn't think he'll be rusty.
"I've played for 12 years in the league so I know how to play basketball," he said. "It's just about getting timing back in the NBA game, so I'm ready. Let's do it."
Senior writers Ramona Shelburne and Marc Stein cover the NBA for ESPN.com. ESPNNewYork.com's Mike Mazzeo and ESPNLosAngeles.com's Arash Markazi contributed to this report.