Travis Williams and Justin Hemphill also added 12 points, and Harrison Wagner chipped in 11.
In a game riddled with turnovers, Arlington Heights coach Josh Welch said his team won by heart.
"That's about it. They just hearted it out," Welch said. "Playing-wise, that was one of our worst games of the year."
McFarland said he'll take the win heading into the Region I semifinals.
"We had a lot of turnovers, but as bad as we played, we came out with a win," McFarland said. "We're going to have to pick it up to move on Friday in the playoffs."
The game looked like it might be a blowout early.
Arlington Heights used a 9-0 run in the first quarter to go up 16-6 after the first quarter.
After just two points in the paint in the first quarter, Southwest started playing more physical defense, and it paid off. The Raiders forced several turnovers to cut Arlington Heights' lead to 28-24 at half.
Tempers flared early in the second quarter when Southwest's Trey Colbert was charged with a technical foul for pushing McFarland.
Midway through the third quarter, Williams was also hit with a technical.
Jordan Boom hit both technical free throws to give Southwest its first lead of the game at 35-34 with four minutes left in the third.
The Raiders extended the lead to 39-36 before Arlington Heights responded with a quick 9-0 run to end the third quarter up 45-39.
Things almost broke out again after Robbie Rhodes' hard foul on McFarland with 4:39 left in the game. After a short altercation, Southwest's Wesley Harris was charged with a technical foul. Both players fouled out of the game on the play.
"They play football against each and basketball against each other." Welch said. "They know each other and have that competitive spirit, which is good, but sometimes it gets out of hand because everyone wants to win."
Williams' technical free throws were part of a 10-2 run to put Arlington Heights up 57-44 with less than five minutes to go.
The Yellow Jackets controlled possession late in the game, and the Raiders never recovered.
Tolbert led Southwest with 13 points, including eight in the fourth quarter.
Arlington Heights will take on Wolfforth Frenship on Friday at The Coliseum in Snyder.