The Yorkshire side's return to the top-flight after a 16-year absence got off to the worst start when defender Robin Koch was penalized for a handball and Mohamed Salah slotted home the resulting penalty kick.
"I love these big matches. To face the best guys in the world is what I do the hard work for at home and in the off-season," Thiem said. "After the first set, it was great tennis from both of us. I could have easily been down two-sets-to-one. I'm really happy to be through. It was a great semifinal."
Meanwhile the arrival of the experienced Manuel Pellegrini at Betis promises the stability that has been missing at the club in recent seasons and that alone should improve a team that underperformed last time around.
Chelsea have been big movers this summer to give Frank Lampard a squad to challenge for the title.
Mikel Arteta has now had time to put his mark on the Arsenal side he inherited from Unai Emery and winning the FA Cup and the Community shield have given the club a positive air, as have the signings of Willian from Chelsea, central defender Gabriel from Lille and the return of Dani Ceballos on loan from Real Madrid.
Although it could be hard to imagine a worse summer than FC Barcelona, Valencia fans will argue that no matter how bad things got at the Camp Nou, they are a lot worse at their Mestalla Stadium.
Adi Hutter's men gained momentum and sealed the deal five minutes later after Silva set up for Dost, who netted the 2-0 lead with a header from close range.
Starting at 8:30 a.m. local time, the event on Sunday features a full marathon, half-marathon and a 10km run, according to the organizers.
The lower league side had their goalkeeper Jakub Jakubov to thank as he defused the promising efforts on target from Andrej Kramaric and Christoph Baumgartner before the break.
Flick claims only to have 16 quality players, including the trouble-causing cases.
Elsewhere, Sheffield United impressed in their return to the top-flight last season and now need to repeat that in what could be a tough second season, Burnley will continue to present teams with a physical challenge under Sean Dyche, while Danny Ings' goals will play a major role in determining Southampton's fate.