Santiago Urrutia and Ed Jones will enter next weekend's Indy Lights double-header finale separated by a point, while other title hopeful Dean Stoneman's chances faded at Watkins Glen.
Former GP3 Series driver Urrutia's 16-point lead heading into the single Watkins Glen race was sliced into by Carlin driver Jones on Saturday, as Urrutia failed to maintain the race lead from pole.
The Uruguayan was passed by eventual winner Zach Veach on the first lap, and a front-right tyre blowout on lap 18 of 25 meant he finished last of all.
Jones' second-place finish means Schmidt Peterson Motorsports' Urrutia now leads the standings by a single point from Jones, with Stoneman a further 22 back.
Briton Stoneman struggled to manage his tyres and opted to pit from his seventh on track for fresh rubber, ultimately taking 11 points for finishing 10th, plus the bonus point for fastest lap.
The final round of the season at Laguna Seca will feature a maximum 66 points on offer across the two races - 30 points for each race win, a point each for pole position, a point for each fastest lap and a point each for most laps led.
With just one point separating the top two, qualifying on pole position, leading the most laps of a race or claiming fastest lap could be instrumental in deciding the title.
To guarantee himself the title, Jones must outscore Urrutia by two points or more. If the two are tied, Urrutia's current four wins to Jones' two would mean Urrutia would still be victorious.
In order for Stoneman to win, he must outscore Urrutia by 24 points and Jones by 23.
RESULTS - 25 LAPS:
|1||Zach Veach||Belardi Auto Racing||40m01.9326s|
|3||Andre Negrao||Schmidt Peterson Motorsports||4.1322s|
|4||Kyle Kaiser||Juncos Racing||6.0913s|
|6||Shelby Blackstock||Andretti Autosport||14.7333s|
|8||Garett Grist||Team Pelfrey||41.1031s|
|9||Zachary Claman||Juncos Racing||1m09.5228s|
|10||Dean Stoneman||Andretti Autosport||1m29.6110s|
|11||Dalton Kellett||Andretti Autosport||1 Lap|
|12||Santiago Urrutia||Schmidt Peterson Motorsports||1 Lap|
LEADING CHAMPIONSHIP STANDINGS: