The 30-year-old Indian, who has made sure of his PGA Tour card for 2018, now sits on the borderline of making it to the third leg.
Lahiri is now 66th on the FedExCup standings and needs to stay inside Top-70 to be able to qualify for the third leg of the Play-offs.
He will need to finish Top-3 to make it to the final 30 for the Top-30 and needs to be 41st or better to make the grade for the third leg.
Tomorrow, Lahiri tees off alongside Russel Knox of Scotland and Bad Cauley from the 10th tee in the afternoon.
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Also on stake for Lahiri is a place on the International Team for the President's Cup. Currently he is 16th and needs to be inside Top-10 for automatic qualification, though he would have another chance to make the team through the two Captain's Picks, which will be announced in early September.
Lahiri has been playing well the last few weeks but those have not translated into results. He has been fine from tee to green, but on the green he has been missing too much, particularly small putts inside 8-10 feet.
Johnson now tops the FedExCup points list, ahead of Spieth, who is in second position, Justin Thomas in third, Hideki Matsuyama in fourth and Jon Rahm in fifth.
The top 100 players in the FedExCup Playoffs will be cut to the low 70 for the BMW Championship, which will be held after a one-week break.
Three winners of the Dell Technologies have gone on to win the FedEx Cup since the Playoffs began in 2007: Vijay Singh in 2008, Henrik Stenson in 2013, and Rory McIlroy last year.