Scott Dixon ended the third and final practice session just ahead of Ryan Hunter-Reay, in what was a busy session around the iconic Long Beach street course.
Due to overnight rain, the circuit had lost some of its grip from the previous day, presenting the 21 drivers with tricky conditions as they aimed to finalise their preparations ahead of qualifying.
Four-time champion Dixon only managed to end the session 0.0002s ahead of Hunter-Reay, with both drivers trading the top spot with a whole host of other drivers throughout the 45 minutes of track action.
Reigning champion Simon Pagenaud was the fastest Chevrolet-powered car in third position for Penske, ahead of James Hinchcliffe.
Initially Hinchcliffe was fastest overall, only for a suspected gearbox issue to materialise on his car, forcing him to slow drastically and eventually stop his car in one of the vast run-off areas around the circuit.
Former Long Beach race winner Takuma Sato was fifth fastest, following on from his competitive pace in practice earlier in the weekend.
Graham Rahal was one of the drivers who produced the initial benchmark at the start of the session, but could only manage seventh overall, ahead of the Penske duo of Will Power and Josef Newgarden.
Sebastien Bourdais endured a tough final practice for Dale Coyne Racing, ending proceedings ninth overall after making minor contact with the wall at Turn 2 during the early stages of the session.
The Frenchman’s incident caused the only red flag delay, and he was lucky to escape with minimal front-wing damage.
Alexander Rossi rounded out the top 10, ahead of veteran Helio Castroneves and Charlie Kimball. The reigning Indianapolis 500 champion has been competitive all weekend, and will be looking to remain so heading into qualifying.
Further down the order veteran Tony Kanaan could only manage five laps on his way to 15th overall, after being plagued by electrical issues throughout the majority of the session.
Meanwhile Marco Andretti and Max Chilton also struggled somewhat, ending final practice 17th and 19th respectively.
