ON THE MORNING of Dec. 3, 2017, Geno Smith took the field as the starting quarterback for the New York Giants. He was greeted by Giants fans who had made the 3,000-mile trip to the Oakland Coliseum.

“That’s my quarterback! That’s my quarterback!” they screamed. Except they weren’t talking about Smith.

Giants fans, dressed in their No. 10 Eli Manning jerseys, had “Fire McAdoo” signs. They wanted head coach Ben McAdoo out. The final straw was McAdoo’s decision to have Smith, notorious in New York thanks to his tumultuous tenure with the Jets, start on that sunny, late fall afternoon in place of Manning.

“It was wild. [Down] to the smell. To the noise. It was nuts,” said Sterling Shepard, then a second-year wide receiver with the Giants.

New York was a team tearing apart at the seams just months after what stands as its only playoff appearance of the last decade. The Giants were 2-9 and now going to bench their two-time Super Bowl champion quarterback not for the heir apparent in Davis Webb, but for Smith.

According to multiple sources with direct knowledge of the situation, McAdoo told Manning at the beginning of the week that he wanted him to start but would probably turn to Smith at some point in part because of a struggling offensive line facing Oakland’s fierce pass rush of Khalil Mack and Bruce Irvin.

Manning, who had topped 225 passing yards just once and been sacked 14 times in his previous seven starts, said if he didn’t know he was going to finish the game, he didn’t want to play. It wouldn’t be fair to Smith to come off the bench after not playing a full game in two-plus years.

This was Smith’s first and only start with the Giants. The 24-17 loss — during which Smith threw for 202 yards and a touchdown with two lost fumbles — was tainted by the dysfunction of the organization.

“I remember [Smith] being really pissed in the locker room afterwards. You can really tell [that game] meant a lot to him,” former vice president of player evaluation Marc Ross said. “I do remember that specifically. The whole situation was just f—ed up. There was so much dysfunction going on then. There was no easy way to move on from [Manning]. It was just messed up.”

The next day, McAdoo and Giants GM Jerry Reese were fired. Manning was reinstated as the starting quarterback, and Smith went back to the bench.

“[Smith] handled it well,” Manning told ESPN in a phone conversation this week. “Went in there, discussed it, talked about it, and he dealt with it like a pro. Just went with it.”

It would be almost four full years until Smith got another chance to start.

Now, 1,792 days later, playing the best football of his professional career with the Seattle Seahawks, Smith will face his former team for the first time as a starter.

“It was just a chance for me to go out there and show what I got,” Smith said Thursday. “It was one game. Obviously there was a lot of speculation and stuff surrounding that game, but for me, like I’ve always been, I was just focused on the game. I didn’t really get caught up in anything else.”

THE DECISION TO start moving on from Manning was one that had been in the works for weeks, according to a source with direct knowledge of the situation. There were a lot of discussions at many different levels, including ownership.

On Monday, Nov. 27, six days before the game against Oakland, McAdoo told Manning the Giants were going to play Smith. Manning slept on it, and there was another discussion the following morning when he told McAdoo he would rather Smith start than have the indignity of being pulled midgame.

At 7:30 a.m. Tuesday morning, Manning walked into the quarterbacks room where Smith and Webb were already working. With tears in his eyes, he told them Smith was going to start Sunday.

“He came down there and it was hard for him to speak about it,” said Webb, who is back this season for his second stint with the team. “He told us what was going to happen. After he was done and finished, it was weird, [McAdoo, offensive coordinator Mike Sullivan and quarterbacks coach Frank Cignetti] walked in a minute after.”

The coaching cognoscenti had one-on-one conversations with each quarterback. Word spread quickly throughout the building.

The Giants were benching Manning, whose streak of 210 consecutive starts was the second longest for a quarterback behind Brett Favre’s 297 (Philip Rivers has since passed Manning with 240).

“Walking in this building, you could just feel it,” Shepard said. “It kind of flowed throughout the building. By that time, everybody already knew what was about to go down. You could feel it in the locker room. You could feel it the whole week.”

Webb, a third-round pick out of California, was the presumed heir apparent but needed more time to prepare as a starter. Smith was a Jets outcast who still had the stench of being a failed savior.

Not that it mattered. Interim coach Steve Spagnuolo — with a nudge from ownership — went back to Manning the following week, and Manning started all 16 games the following season.

“It was just the wrong city, the wrong place for him to go to really have a chance — New York City, Eli Manning. It was just way too much for him. He caught the stream,” Ross said. “For Geno, there was still that stigma about Geno. He’s removed from it now. So [the fans] have a whole different opinion, or no opinion.”

SMITH FINDS HIMSELF once again succeeding a quarterback who was once the face of the franchise. This time, though, there’s no turning back.

When Russell Wilson and his new team, the Denver Broncos, came to Seattle to open the season, it was supposed to be Wilson’s moment. After what became a nasty divorce between quarterback and team, Wilson got a new home — and a lucrative new deal — and returned to Lumen Field to kick off Week 1.

The Seahawks got former Broncos second-round pick Drew Lock in the Wilson trade. Lock was presumed the likely starter until Smith beat him out in training camp.

“They wrote me off. I ain’t write back, though,” Smith said in his on-field postgame interview after a 17-16 win over the Broncos. “That’s the problem. I ain’t write back.”

Smith has the Seahawks in first place in the NFC West at 4-3 following a win over the Los Angeles Chargers. He leads the league with a 73.5% completion percentage while still being tied with Buffalo’s Josh Allen for the most touchdown passes of 20-plus air yards (six). He has the fourth-highest QBR (66.8), behind only Patrick Mahomes, Allen and Tua Tagovailoa, respectively.

“I’m not surprised,” Manning said. “Geno was always talented. Had a big arm. Could make all the throws. Looked down the field well. Threw the ball down the field extremely well.

“Like any quarterback it’s just learning defense, getting comfortable within your offense, just kind of understanding where your problems are.”

It took almost four years to get another start, a remarkable eight years between being a full-time starter with the Jets and the Seahawks. He’ll face one of his toughest matchups of the season when he hosts his former team Sunday in the 6-1 Giants.

“I don’t have any remorse or anything,” Smith said. “Just looking forward to going out there and competing again.”