Timo Werner gave Joachim Low's men an early lead and Omar Othman's unfortunate own goal undermined Saudi Arabia as they briefly threatened to find a way into the contest.
Marco Reus made his first international start since March 2016 and dazzled during the first half, laying on Werner's opener and linking pleasingly with the RB Leipzig striker and Thomas Muller.
A former Dortmund team-mate of Reus' will enter Russia 2018 under a cloud – Ilkay Gundogan again receiving boos following his meeting with Turkish president Recep Tayyip Erdogan.
Saudi Arabia were humiliated 8-0 in the 2002 World Cup by Germany but their current vintage, led by former Chile coach Juan Antonio Pizzi, should fare better this time around, with seemingly vulnerable hosts Russia up first for them in the tournament opener.
Fahad Almuwallad and Yahia Alshehri both threatened in attack and Taiseer Aljassam reduced the arrears in the 84th minute after the goalscorer was brought down by Sami Khedira and Marc-Andre ter Stegen saved fellow substitute Mohammed Alsahlawi's penalty.
Reus was alert to Joshua Kimmich's raking eighth-minute pass and cushioned a volley back across goal to give Werner a simple finish.
A crisp 20-yard shot from Reus then cannoned back off the post and Germany's only hindrance during the opening half hour was a well-functioning Saudi offside trap.
Some stylish interplay with Muller and a clever chipped backheel by Reus saw Werner head wide in the 32nd minute – the ball not dropping for the volley he craved.
A combination of Abdullah Almuaiouf and the Saudi goalkeeper's right-hand post denied Khedira from Reus' right-wing cross, but the visitors almost levelled when Almuwallad fizzed Alshehri's cutback just past the post.
Striker Almuwallad was unable to turn home from close range as Saudi Arabia's counter-attacking threat became increasingly prevalent.
But their chances of springing a surprise were dealt a body blow two minutes before the break when a patient and incisive Germany move ended with Othman putting Werner's cross into his own net under pressure from Muller.
Almuaiouf made a brilliant reaction save from Julian Draxler in the 50th minute after the Paris Saint-Germain winger was precisely picked out by Jonas Hector and Saudi Arabia's number one continued to excel by tipping a powerful Muller strike behind.
Gundogan was whistled despite Low's protestations to the stands when he came on for the excellent Reus in the 57th minute.
Jeers almost turned to cheers moments late as Gundogan avoided the offside flag but Almuaiouf smothered the chance.
The flow of second-half substitutes disrupted Germany's rhythm and Alshehri twice went close.
Bayer Leverkusen favourite Julian Brandt – surprisingly preferred to Leroy Sane by Low in his final 23 – made a lively cameo and sent a volley wide at the back post.
The wealth of talent at Germany's disposal is beyond doubt but, as Aljassam reduced the arrears and Mats Hummels avoided giving away a second penalty despite grabbing a handful of Alsahlawi's shirt, it became clear they must lift their level in Russia.