Lucien Favre then brought on Marco Reus for his return after a long injury lay-off, and the German international paid back his trust seconds later, beating Weinkauf following a free-kick at the hour mark.
Finland's six-time champions KuPS Kuopio will face the Lithuanian champions FK Suduva in the third round of the Europa League Qualifiers. Enditem
"Players like Riqui have something special, but it is going to be very complicated for him here as there is a lot of competition. I have told him that he has a future here, and we will think about what is the best way to succeed at Barca," he added.
15th seed Grigor Dimitrov of Bulgaria eased past Italian wildcard Gianluca Mager 7-5, 6-1, while Marin Cilic rallied to beat Kazakhstan's Alexander Bublik 6-7 (4), 6-2, 6-4 to set up a second round meeting with sixth seed David Goffin.
The Arsenal captain scored a brace in last season's FA Cup final as Arsenal came from behind to beat Chelsea 2-1. He also netted in Arsenal's 3-0 victory over Fulham last Saturday in their first game of the new Premier League season.
Hoffenheim dominated possession and produced more promising chances but Horn was on guard to deny Kramaric and Pavel Kaderabek in the 18th minute.
Djokovic beat his fellow Serb Filip Krajinovic 7-6 (7), 6-3, while Nadal won 6-1, 6-3 against Dusan Lajovic, also of Serbia.
"I spoke to him yesterday (Friday) before training; I think that the young players have to play regularly and that is what I told him," Koeman commented, adding that the same went for Carles Alena and new signing Pedri.
Cologne had the worst possible start on home soil as Jonas Hector's return pass was intercepted by Kramaric, who kept his cool and nutmegged goalkeeper Timo Horn for the opener with only three minutes gone.
With Li Shenglong's header in the 75th minute, Shanghai SIPG beat Chongqing Lifan 3-2.
Just three minutes into the second half, Hamdallah doubled his team's lead and his own tally after tapping in a rebound that fell to him just outside the six yard box, after a magnificent solo run down the right by Khalid Al-Ghannam ended with his initial shot being deflected into the Moroccan's path.