The NTT IndyCar Series championship has become a two-horse race as the title chase has reached its halfway mark.

Emerging as contenders for the championship are Team Penske's Josef Newgarden and Andretti Autosport's Alexander Rossi.

The numbers show that the American pair have displayed unvarying contention week in and week out by logging an average finish of 5.4 and 5.9 respectively.

Newgarden's Penske perfect performances act as a return to form after a somewhat disappointing 2018 season. He came out of the gate roaring with a win at the season opener at St. Petersburg and solidified his championship hopes with four straight top-five finishes.

The Hendersonville, Tennessee native lost the points lead to teammate Simon Pagenaud after the Month of May when Pagenaud swept the IndyCar Grand Prix and the Indianapolis 500. Newgarden led a hearty amount of both races, but a pitstop problem took him out of contention of the GP, and couldn't contend with the top combatants of Takuma Sato, Rossi and Pagenaud in the waning stages of the 500 before finishing fourth.

He endured the highest highs and the lowest lows in the next three rounds as strategy elevated him to wins in a rain-shortened Detroit race 1 and a close win over Rossi at Texas. The low point came in Detroit Race 2 when a crash with James Hinchcliffe.

He stands 25 markers ahead of Rossi heading into Road America.

The next batch of races favour the 28-year-old American as he has won at six of the final eight tracks, including Road America where he is the defending race-winner. Newgarden acknowledged that while the odds are in his favor, he cannot let his guard down given the ever-changing landscape of IndyCar.

"There's tracks where you're historically good, you go there and have an off year," he said. "Things change, tires change, the car changes. We've just got to stay alert and aware of where we're good and where we're not.

"What I mean by that is, it's never guaranteed where you're going to be good for the second half of the season. I think you just got to be open-minded that there might be some tracks we weren't good at in the past, maybe we're good at this year, just capitalize when you can. You have to take advantage of the opportunities when you have a good car."

If you are looking for a worthy championship adversary, then look no further than Alexander Rossi.

Rossi scored a win at Long Beach in April and has six extra top fives to his credit. He has ended up bridesmaid three times as of late starting with the Indy 500 where he dazzled with several daring moves and overcame a fueling miscue to put himself in contention for the race win.

He came up short to Simon Pagenaud which started a runner-up trend with seconds coming at Detroit Race 1 and Texas.

His second place finishes have come at the expense of a Team Penske driver with Pagenaud holding off a valiant charge by Rossi and Newgarden taking the other two victories which has put him on notice.

"When you have a Penske Chevrolet driven by someone as good as Josef, there's only so much you can do, he said. "Yeah, it sucks. I mean, we're always there, but we're always playing the bridesmaid as of late."

The lone blemish on the 27-year-old Californian's record is a 22nd at the IndyCar GP when he crashed with Patricio O'Ward on the opening lap.

There were a couple of occasions where things could have gone south for Rossi at COTA and Detroit Race 2. A late yellow killed his strategy at COTA and he nearly was taken out in the same crash that eliminated Newgarden.

He salvaged ninth at COTA and fought his way to fifth at Detroit in order to keep the damage to a minimum. With eight rounds left in the season, Newgarden and Rossi are easily the prime title candidates with their near picture-perfect seasons.

That being said, it is still nearly impossible to make a substantial bet on who will hoist the Astor Cup at WeatherTech Raceway Laguna Seca in September.

That is not to say that a few things are certain. Newgarden's performance in the first nine rounds proves that he can win under any circumstance and Rossi has demonstrated that he can pull himself into contention before it is all said and done.