Takuma Sato and Will Power topped both of IndyCar's test sessions at Phoenix on Saturday, while four-time champion Scott Dixon spun and clipped the wall.
Tony Kanaan's AJ Foyt Racing-Chevrolet sat at the top of the speed chart for much of the evening session but, with 75 minutes to go, Power - who had been at the bottom of the times doing long runs - went out on a fresh set of tyres in his #12 Penske-Chevrolet and sprang to the top.
Power was then deposed at the top of the times by Sato less than 10 minutes later, the Rahal Letterman Lanigan Racing driver setting a best time of 19.3790s.
Sato and Power had earlier set the pace in the afternoon session, with Japanese driver's benchmark time a 19.3920s.
"The open test was very successful, I would say," said Sato.
"Lots of things done and lots of things to be tried, and I think over the course of two days we learned a lot.
"[It's a] great car, definitely more exercise for the drivers, definitely busier with low downforce."
Kanaan's earlier benchmark was enough for him to keep hold of third, ahead of reigning champion Josef Newgarden in the #1 Penske-Chevrolet.
Marco Andretti and Alexander Rossi (both pictured above) were fifth and sixth for Andretti Autosport-Honda, and were the final drivers to record laps above the 189mph threshold.
On track action became more frantic in the final 40 minutes of the session following a track inspection as drivers practiced running in traffic.
Dixon appeared to get too close to a car in front and spun in his #9 Chip Ganassi Racing-Honda, making light contact with the Turn 1 wall.
"It was our second or third lap out of the pits," said Dixon. "A couple of the Andretti cars got by and were a little bit slower.
"I got low in [Turns] 1 and 2, touched the throttle and had a bit of a run and lost the rear."
Dixon's best time gave him seventh ahead of last year's Phoenix race winner, Simon Pagenaud, while Spencer Pigot put in a competitive run to end the day ninth fastest in his #21 Ed Carpenter Racing-Chevrolet.
Dale Coyne Racing's Pietro Fittipaldi was an impressive 10th, and top rookie.
AJ Foyt's second driver, rookie Matheus Leist, had whitewalled his tyres at the same spot that Dixon crashed at in the day's earlier test session and also spun there on Friday.
The Brazilian brushed the Turn 4 wall twice later on in Saturday's evening session, but finished the day with the 12th fastest time.
Carlin's Charlie Kimball and Max Chilton were 14th and 16th respectively, sandwiching the second Ganassi of Ed Jones, while Schmidt Peterson Motorsports duo James Hinchcliffe and Robert Wickens were at the bottom of the speed charts.
Afternoon session times
|1||Takuma Sato||Rahal Letterman Lanigan||Dallara/Honda||19.3920s||-||63|
|2||Will Power||Team Penske||Dallara/Chevrolet||19.4383s||0.0463s||51|
|3||Scott Dixon||Chip Ganassi Racing||Dallara/Honda||19.5207s||0.1287s||50|
|4||Ryan Hunter-Reay||Andretti Autosport||Dallara/Honda||19.5358s||0.1438s||39|
|5||Simon Pagenaud||Team Penske||Dallara/Chevrolet||19.5371s||0.1451s||49|
|6||Sebastien Bourdais||Dale Coyne Racing||Dallara/Honda||19.5746s||0.1826s||45|
|7||Ed Jones||Chip Ganassi Racing||Dallara/Honda||19.6019s||0.2099s||81|
|8||Josef Newgarden||Team Penske||Dallara/Chevrolet||19.6216s||0.2296s||32|
|9||Matheus Leist||AJ Foyt Enterprises||Dallara/Chevrolet||19.6296s||0.2376s||50|
|10||Alexander Rossi||Andretti Autosport||Dallara/Honda||19.6410s||0.2490s||39|
|11||Graham Rahal||Rahal Letterman Lanigan||Dallara/Honda||19.6468s||0.2548s||72|
|12||Marco Andretti||Andretti Herta||Dallara/Honda||19.6760s||0.2840s||15|
|13||Robert Wickens||Schmidt Peterson Motorsports||Dallara/Honda||19.7495s||0.3575s||48|
|14||Pietro Fittipaldi||Dale Coyne Racing||Dallara/Honda||19.8291s||0.4371s||64|
|15||Tony Kanaan||AJ Foyt Enterprises||Dallara/Chevrolet||19.8325s||0.4405s||17|
|16||Zach Veach||Andretti Autosport||Dallara/Honda||19.9084s||0.5164s||54|
|18||Spencer Pigot||Ed Carpenter Racing||Dallara/Chevrolet||20.0428s||0.6508s||54|
|20||Ed Carpenter||Ed Carpenter Racing||Dallara/Chevrolet||20.1436s||0.7516s||56|
|21||James Hinchcliffe||Schmidt Peterson Motorsports||Dallara/Honda||20.2463s||0.8543s||91|
|22||Gabby Chaves||Harding Racing||Dallara/Chevrolet||20.7197s||1.3277s||27|
Evening session times
|1||Takuma Sato||Rahal Letterman Lanigan||Dallara/Honda||19.3790s||-||158|
|2||Will Power||Team Penske||Dallara/Chevrolet||19.3878s||0.0088s||135|
|3||Tony Kanaan||AJ Foyt Enterprises||Dallara/Chevrolet||19.4018s||0.0228s||65|
|4||Josef Newgarden||Team Penske||Dallara/Chevrolet||19.4257s||0.0467s||121|
|5||Marco Andretti||Andretti Herta||Dallara/Honda||19.4658s||0.0868s||118|
|6||Alexander Rossi||Andretti Autosport||Dallara/Honda||19.4729s||0.0939s||107|
|7||Scott Dixon||Chip Ganassi Racing||Dallara/Honda||19.5152s||0.1362s||79|
|8||Simon Pagenaud||Team Penske||Dallara/Chevrolet||19.5763s||0.1973s||125|
|9||Spencer Pigot||Ed Carpenter Racing||Dallara/Chevrolet||19.6425s||0.2635s||74|
|10||Pietro Fittipaldi||Dale Coyne Racing||Dallara/Honda||19.6521s||0.2731s||118|
|11||Graham Rahal||Rahal Letterman Lanigan||Dallara/Honda||19.6608s||0.2818s||137|
|12||Matheus Leist||AJ Foyt Enterprises||Dallara/Chevrolet||19.7169s||0.3379s||94|
|13||Zach Veach||Andretti Autosport||Dallara/Honda||19.7560s||0.3770s||120|
|15||Ed Jones||Chip Ganassi Racing||Dallara/Honda||19.7645s||0.3855s||107|
|17||Gabby Chaves||Harding Racing||Dallara/Chevrolet||19.9229s||0.5439s||86|
|18||Ed Carpenter||Ed Carpenter Racing||Dallara/Chevrolet||19.9759s||0.5969s||66|
|19||Ryan Hunter-Reay||Andretti Autosport||Dallara/Honda||20.0313s||0.6523s||101|
|20||Sebastien Bourdais||Dale Coyne Racing||Dallara/Honda||20.0785s||0.6995s||92|
|21||James Hinchcliffe||Schmidt Peterson Motorsports||Dallara/Honda||20.0983s||0.7193s||71|
|22||Robert Wickens||Schmidt Peterson Motorsports||Dallara/Honda||20.1590s||0.7800s||102|