O’Brien, 20, was called up to make his AFL debut against the Brisbane Lions after Jacobs was ruled out with an ankle injury. It was the first game the durable Jacobs has missed in four years, ending his streak of 93 consecutive AFL matches.
O’Brien has been waiting for an opportunity for two of those years. The promoted rookie has established himself as one of the premier ruckmen in the SANFL since being recruited by the Crows in December, 2014.
Prior to Saturday night, O’Brien had impressed in NAB Challenge games and come close to selection as an emergency, but the form of Jacobs had held him out of Adelaide’s best 22.
Instead of becoming frustrated, the level-headed Crow embraced the virtue of patience.
“I just try and live by (the mantra) ‘Be ready’ – that’s my motto,” O’Brien said.
“Anytime, ‘Sauce’ (Jacobs) could go down and I could go in. I’m happy to be waiting in the wings and learning my craft in the SANFL.
“To get an opportunity tonight was awesome but, hopefully, Sauce is back in soon.”
As predicted, the competitive O’Brien adapted well to AFL football.
The former Calder Cannons junior won 29 hit-outs, 16 possessions (nine contested), four clearances and also kicked a goal in Adelaide’s 138-point win over the Lions.
O’Brien credited mentor Jacobs with helping to prepare him for his debut.
“It was awesome. I loved every minute of it and, hopefully, there are a few more to come,” he said.
“It’s obviously a fair jump. The boys made it a lot easier for me tonight – they were awesome. ‘Sauce’ prepared me for it during the week, and the same with ‘Doc’ (Matthew) Clarke.
“I blew up a fair bit! The ball goes quick end-to-end.
“It was pretty tough physically, but I got through it in the end, which was nice.”
O’Brien’s first AFL goal came in the third quarter when he took a mark inside forward 50m.
It followed a missed attempt in the first quarter.
The Crows players mobbed the popular 201cm, 100kg, ruckman after his set shot sailed through.
“I had an earlier opportunity, which would’ve been nice to kick, but eventually, I got one,” he said.
“The boys just told me to take my time and go through my routine. It was awesome. The boys got around me and I nearly fell over there, but managed to keep my feet!”
The clash between the Crows and Lions pitted a first-gamer in O’Brien against second-gamer Archie Smith in the ruck. It wasn’t O’Brien’s first battle against athletic former basketballer Smith.
“I played against Archie in Under-18s in the state carnival. He was playing for Queensland and I was playing for Vic Metro,” O’Brien said.
“He’s always had that big leap, so it was a bit of a challenge coming up against him. I’ve got great respect for him and he’s going to be a good player.
“Hopefully, we have a few more duels in the future.”
O’Brien was part of a strong team performance by the Crows, who dominated the young Lions team for the duration of the game to record an important and percentage-boosting victory.
“Pykey (coach Don Pyke) was on about playing our way for four quarters. I think we really did that. We didn’t have a lapse, we kept going and had a big win. We were ruthless all night,” O’Brien said.
Crows forward Eddie Betts insisted O’Brien lead the team off Adelaide Oval following the win.
O’Brien received rapturous applause from the crowd of 43,549 fans, and his friends waiting in the change rooms loudly chanted his name as he walked in for the team song. O’Brien’s parents and brothers were also on hand to witness the memorable occasion.
“It was a great reception from the crowd and all the fans. I really appreciated that and it was a great feeling,” he said.
“I don’t know how my mates got into the rooms, but they snuck themselves in and gave me a big roar when I came in. That was awesome.
“It was great to spend time with my friends and family after and enjoy the moment with them.”
O’Brien will now have to wait and see whether he receives another opportunity against Fremantle at Domain Stadium on Sunday. Jacobs hopes to prove his fitness at training later in the week.
“We want to get Sauce’s ankle right coming into the business end of year.
“If he’s ready, he’s ready. We will see.”