Audi driver Ekstrom, 29, has led the championship since the first race of the season, ironically also at Hockenheim.
Despite failing to add to his wins tally since then, the Swede, who is bidding to add to his 2004 title, has been a model of consistency, with five podium finishes cementing his place at the top of the table.
"I'm looking forward to the finale at Hockenheim," said Ekstrom. "I won the first race there at the start of the year. I can hardly wait to return and to fight for the championship. It'll be a tough race."
Green's win, Ekstrom's title
AMG Mercedes driver Spengler, 24, lies only two points behind Ekstrom after his second place at Barcelona, a race that saw furore as Audi withdrew all their cars after the Swede was punted off, deliberately perhaps, by tail-ender Mathias Lauda.
After failing to score points in the first three races of the season, he has recovered and will win the title if he claims victory, as he did last year, at Germany's cathedral of speed.
"The championship is open in the final race. I hope for an exciting and fair battle with the other two title contenders and in the end I want one more point than them," said the Canadian.
The third of the title contenders, Martin Tomczyk, 25, is the form man. Wins at Zandvoort and the Nurburgring brought him right onto Ekstrom's tail and he lies just four points behind his team-mate.
That means that to win the title he would need to win the race with Spengler between him and Ekstrom.
And he knows that it is still all up for grabs.
"Nothing is decided yet," Tomczyk said. "The championship leaders are even closer together going into the last race. We can look forward to an exciting finale.
"We have the lead and, if we have things our way, want to finish first and second in the championship for Audi."
Aside from the title battle, this weekend will see one other significant event as Germany's Christian Abt competes in his last race before retiring from the driving seat.
The 40-year-old Phoenix Audi man has raced in every one of 83 DTM races since the championship was re-launched in 2000. Only Bernd Schneider can match that record.