The Southland motorcycle rider emerged as a leading contender before a crashed rider flung gravel which sent Buchanan into orbit at pace and derailed his campaign.
The 19-year-old suffered back and rib injuries, which forced him to battle through pain and accept P18 in the Moto3 World Championship’s main event.
While it was not the race Buchanan expected, he still rated the event as his "best weekend in the world championship to date".
"From the very first session in FP1 I was fast in the wet and then the following two dry sessions I had the top two in both of those," Buchanan said.
"I felt really strong and my race pace was there to be the fastest.
"In FP2 a rider had crashed the lap before and they didn’t put out any flags to warn me of the gravel on the corner, so when I went in, I had an off-throttle high side.
"The impact was really strong and it caused a lot of force on my ribs and back. I knew immediately something wasn’t right."
His challenges were compounded by another high side in qualifying, staged nine hours later due to a sink hole on the circuit’s main straight needing repair.
"It was a massive effort from the team and myself having to run back and forth from medical after probably the biggest high side of my life.
"Strangely enough, that wasn’t the one that hurt — I came away with just a black eye.
"I was certainly feeling the effects of the FP2 crash, but the pace was there and I was determined to fight in the race."
Ahead of Sunday’s race, Buchanan was struggling to breath and move his body, aiming to get as much treatment as he could in the short timeframe.
"When I got on the grid I was in a lot of pain, but still the first laps were great and I made up some ground and I felt really comfortable passing people, being patient and saving the tyre because I knew I had the pace.
"Then the adrenaline wore off and I knew it was going to be a really long race. I wasn’t able to breathe properly."
The injuries impacted his riding technique, forcing him to sit further forward on his bike and put more pressure on his front wheel.
"There were so many times I thought about pulling in because the pain was too much, but it was important for me to get a race distance under my belt no matter how bad it was."
When the race was red flagged, a shortened five-lap sprint was ordered to decide the result.
"It was the hardest race of my life to finish, but we did it."
Buchanan’s focus now switches to getting healthy ahead of the Circuit of the Americas in Texas this weekend.
"We’ve still got another 20 races to improve on it.
"It’s not a finished product yet — we still need to polish the diamond. I know that our big moment is coming." — Allied Media
