Marko cites the examples of the British, Azerbaijan and Hungarian Grands Prix as examples that Verstappen should be further ahead in the standings.
The Red Bull driver retired from the British GP while leading after contact with Hamilton, who went on to win the race despite a penalty for the incident.
In Baku, Verstappen also retired while running first with five laps remaining when one of his tyres exploded on the main straight.
And in Hungary he finished down in ninth position after he was hit at the start when Valtteri Bottas overshot the first corner.
"Before the last three races, we actually feared that we would be significantly behind," Marko told Motorsport.com.
"The bottom line is that we scored more points than Hamilton in those grands prix, mainly because of Hamilton's race in Turkey where he was only fifth, while Max finished second in Sochi - certainly by luck as well, because of the rain.
"But even more remarkable is: we innocently lost Baku, lost Silverstone and lost Hungary. If you calculate the amount of points we lost carefully, then it's over 50 points in those three races.
"As a result we are only 12 points ahead now. So we have survived all those setbacks and we have also been able to match the upswing from Mercedes."
Marko believes Verstappen will need at least two more victories in the remaining five races in order to secure his first F1 title.
"Looking at the remaining races, I think we have to win at least two more races to be reasonably safe or, let's say, confident going into the final race," he said.
"The high altitude tracks of Brazil and Mexico should suit us significantly better. It's just that so much has already happened this season.
"So-called Mercedes tracks weren't Mercedes tracks in the end and the same goes for Red Bull tracks."
Asked what are Verstappen's chances of winning the title, Marko said: "If we win the next two races, then it's 60-40 for Max."
Marko says the tiniest of factors can affect the competitive balance between Mercedes and Red Bull, but he feels it's Verstappen and Hamilton who are making the difference.
"It's so balanced that the form of the day, the tarmac and even the temperatures are extremely important," he added.
"It looks like Mercedes is much quicker to get their car to the right set-up. We have a more complex car and on average it takes us longer to do it, but still there are only two drivers who always get the maximum out of it. That's Hamilton at Mercedes and Max with us.
"The number two drivers, Perez thank God is on the up, but also Bottas - he did a sensational race in Turkey and more than average in Austin.
"But in the end these two exceptional drivers keep this duel going, no matter if it's the Mercedes car or the Red Bull that is faster.
"Overall, it's the driver who makes the difference. And those drivers are so strong that Verstappen can also beat a faster Mercedes on hard tyres."