Jordan Spieth insisted at last week's PGA Championship that he was no longer in a slump. For further proof, he went on a birdie barrage Thursday at the Charles Schwab Challenge.

Beginning on the back nine at Colonial Country Club, Spieth made his first red number of the day by pitching in for birdie at the par-3 13th.

The brilliance of @JordanSpieth. ?#QuickHits pic.twitter.com/LjjSeiTIrX

— PGA TOUR (@PGATOUR) May 23, 2019

Spieth then went on a three-hole birdie run, beginning at the par-4 15th.

2nd birdie of the day.@JordanSpieth is off to a strong start @CSChallengeFW.#QuickHits pic.twitter.com/TbZnidFQ7L

— PGA TOUR (@PGATOUR) May 23, 2019

Another birdie for @JordanSpieth.

Spieth knocks it to inside 5 feet to get to -3.#QuickHits pic.twitter.com/CFZiKsumxw

— PGA TOUR (@PGATOUR) May 23, 2019

30 feet. Boom.

Jordan Spieth. Solo leader.#LiveUnderPar pic.twitter.com/CRe4a1lzwZ

— PGA TOUR (@PGATOUR) May 23, 2019

An errant approach shot at the par-4 18th, which landed in a water hazard, led to double bogey at the par-4 18th. Spieth turned in 2 under par, but quickly got back those dropped shots.

He birdied the par-5 first.

Bouncing back.@JordanSpieth makes birdie from a tough spot after doubling the previous hole.#QuickHits pic.twitter.com/SvJzbL5bcp

— PGA TOUR (@PGATOUR) May 23, 2019

This wonderful recovery shot led to birdie at the par-4 second.

Jordan Spieth is doing @JordanSpieth things.

What a birdie from the trees. ?#QuickHits

?: https://t.co/hah4g5wNli pic.twitter.com/SQb7Suh9u4

— PGA TOUR (@PGATOUR) May 23, 2019

And he rolled in this 46-footer for birdie at the par-3 fourth.

Are you kidding?@JordanSpieth from 46 feet. Buckets.#QuickHits

?: https://t.co/hah4g5wNli pic.twitter.com/M5G6Ye2HLi

— PGA TOUR (@PGATOUR) May 23, 2019

Spieth stood at 5 under par through 13 holes, with seven birdies and one double bogey. He dropped a shot at the eighth hole but responded with a birdie at his last, the par-4 ninth, to finish a 5-under 65.

An ideal round of golf for @JordanSpieth.

The 2016 @CSChallengeFW champion opens with a 65.#QuickHits pic.twitter.com/etZxEfMf77

— PGA TOUR (@PGATOUR) May 23, 2019