The 24-year-old attacking midfielder proved why Dortmund paid Shakhtar Donetsk €27.5 million for him with his first two league goals in only his third Bundesliga appearance.
It means Dortmund go into the international break for the forthcoming World Cup qualifiers two points clear of European champions Bayern and finish the weekend as the league's only team with a 100 percent record.
Earlier, VfB Stuttgart romped to a 6-2 Bundesliga win over Hoffenheim with striker Vedad Ibisevic netting a hat-trick after coach Bruno Labbadia was sacked last Monday.
Stuttgart picked up their first points of the season after three straight defeats led to Labbadia's dismissal.
The result lifts Stuttgart out of the bottom three and into 14th and leaves Hoffenheim 11th after their first defeat of the season.
On Saturday, Leverkusen blew the chance to go top with a 2-0 defeat at
resurgent Schalke 04.
Both Germany left-back Dennis Aogo, who has joined Schalke on loan from Hamburg, and Ghana midfielder Kevin-Prince Boateng, who signed a four-year deal after arriving from AC Milan on Friday, started as the Royal Blues picked up their first league win of the season.
Schalke went ahead with half an hour gone when a free-kick went in off midfielder Marco Hoeger's right shoulder before Peru forward Jefferson Farfan made sure of the win when he drilled home an 83rd-minute penalty after being hauled down in the area.
Mainz 05 also wasted their opportunity to go top as they crashed to a 4-1 defeat at Hanover 96.
Mainz took a 12th-minute lead through striker Nicolai Müller, but Senegal striker Mame Diouf and Poland forward Artur Sobiech put the hosts 2-1 up at the break before Ivory Coast forward Didier Ya Konan and midfielder Edgar Prib increased the lead.
Elsewhere, struggling Hamburg picked up their first win of the season after two consecutive defeats with a 4-0 thumping of promoted Eintracht Braunschweig.
Dutch international Rafael van der Vaart put Hamburg ahead in the seventh minute on their first attack before Cameroon striker Jacques Zoua doubled the lead on 17 minutes as the hosts counter-attacked at pace.
Hamburg made sure of the three points, and Braunschweig's fourth straight defeat, to leave Eintracht bottom of the table.
Meanwhile, Borussia Mönchengladbach moved up to seventh as they romped to a 4-1 home win over Werder Bremen.
Wolfsburg enjoyed a 2-0 win at home to Hertha Berlin with Ivica Olic and Diego on target, while Augsburg picked up their second straight win with a 1-0 success at Nuremberg thanks to a late goal from substitute Kevin Vogt.