The top four teams in the Pac-12 South squared off Saturday — USC at Arizona and UCLA at Arizona State — and the results of the inter-division battles were inconclusive.

Both games were decided by a field goal or less, and now three teams sit at the top of the division standings with two losses.

The Wildcats (5-3, 2-3 Pac-12) trail by a game-and-a-half but have the easiest stretch of games remaining.

At the season’s start, No. 18 USC seemed destined to run away with the South title. The Trojans were a trendy national title pick and had the Heisman frontrunner in Matt Barkley. Even with an unimpressive start to the season, USC was still in great shape to run away with the division.

Instead, the Trojans came across the buzz saw known as the Arizona offense. Now the entire Pac-12 south standings are in question.

That’s why, with all four teams playing ranked opponents this weekend, Saturday will come to be known as Separation Day, at least in my book.

Sure, USC still has the superior talent and a half-game division lead with a 4-2 conference record, but they also have a date with No. 2 Oregon.

Unless Barkley and the Trojans run past the Ducks this Saturday, something that’s not very easy to do, they’ll be sitting at 4-3 in the conference and will be losing the tie-breaker to No. 24 Arizona.

The Battle at the Collesium between the Pac-12’s two most notable programs has caused fans and sports writers to salivate all season long, and rightly so. If Oregon wins, they’re in the driver’s seat for the national championship — and if USC wins they’re the South favorites once again.

But don’t be mistaken, it’s not the only marquee matchup happening in Los Angeles on Saturday.

No. 25 UCLA hosts the Wildcats in what will be a deciding factor for how the division will play out. A victory by the Bruins would put them at 4-2 in conference, but they have USC coming to the Rose Bowl two weeks later. A victory for the Wildcats would mean so much more.

Three weeks ago it was laughable to think Arizona would still be in the hunt for the Pac-12 title game — it’s hard to be a serious contender with a 0-3 conference record.

But if Arizona beat the Bruins, and especially if USC also loses, the Wildcats will control their own destiny.

If the Wildcats do manage to beat a good UCLA team on the road and finish their murderer’s row of a schedule with a 3-3 record, they really should be the favorite to win the division.

Including Saturday’s game, the UA’s FCS opponents have a 49-14 record and six of the eight teams have been ranked at some point this season.

The two non-ranked games include an overtime win against Toledo (8-1) and a 52-17 shellacking of a previously ranked Washington team.

Compare that to the 9-15 record of Arizona’s final three opponents — Colorado, Utah and ASU — and the Wildcats would be sitting in a good position if they can get past the Bruins. That’s a pretty big if, though.

The other team in this four-horse race is the constantly overlooked Sun Devils.

The path for ASU looks dicey at best. They first have a huge game this weekend at No. 13 Oregon St. and still have USC and Arizona on the slate.

At worst, ASU can play spoiler to either the Trojans or the Wildcats down the stretch.

1. No. 4 Oregon (8-0, 5-0 Pac-12) Last week: 1
Week nine: (W 70-14 against Colorado)
This Week: at No. 17 USC

2. No. 11 Oregon State (6-1, 4-1) LW: 2
Week eight: (L 20-17 at Washington)
This Week: against Arizona State

3. No. 14 Stanford (6-2, 4-1) LW: 4
Week nine: (W 24-17 against Washington State)
This Week: at Colorado

4. No. 22 Arizona (5-3, 2-3) LW: 5
Week nine: (W 39-36 against USC)
This week: at UCLA

5. No. 17 USC (6-2, 4-2) LW: 3
Week nine: (L 39-36 at Arizona)
This Week: against No. 4 Oregon

6. UCLA (6-2, 3-2) LW: 6
Week nine: (W 45-43 at Arizona State)
This Week: against No. 22 Arizona

7. Washington (4-4, 2-3) LW: 8
Week nine: (W 20-17 against Oregon St.)
This Week: at Cal

8. Arizona State (5-3, 3-2) LW: 7
Week nine: (L 45-43 against UCLA)
This Week: at No. 11 Oregon State

9. Utah (3-5, 1-4) LW: 10
Week nine: (W 49-27 against Cal)
This Week: against Washington State

10. California (3-6, 2-4) LW: 9
Week nine: (L 49-27 at Utah)
This Week: against Washington

11. Washington State (2-6, 0-4) LW: 11
Week nine: (L 24-17 at Stanford)
This Week: at Utah

12. Colorado (1-7, 1-4) LW: 12
Week nine: (L 70-14 at Oregon)
This Week: against No. 14 Stanford