The playmaker was back at the Partizan Stadium, Belgrade - where we drew 0-0 against Partizan in the Europa League in September - and played a key role in the Danes' victory.
Serbia went ahead through Zoran Tosic and led 1-0 at half-time before Denmark turned the game around in the second half.
Christian fired in a shot that Vladimir Stojkovic could only parry out to Niclas Bendtner for 1-1 and then provided the free-kick for Simon Kjaer to head home for 2-1. Bendtner completed the turn around with his second as Denmark jumped to the top of Group I.
Vlad Chiriches helped Romania to top spot in Group F of Euro 2016 qualfying with a 2-0 win over Northern Ireland in Bucharest on Friday night.
The central defender kept a clean sheet and went closest to breaking the deadlock in the first half when his overhead kick was saved by Roy Carroll.
Romania eventually won it thanks to a double from Paul Papp after 74 and 79 minutes.
Romania top the group by a point from Northern Ireland and their next qualifier is against Faroe Islands - who shocked Greece 1-0 on Friday night - in March, 2015.
Ahead of that, Vlad and Christian are set to meet when Romania host Denmark in a friendly on Tuesday.
In friendly action, Hugo Lloris made a number of saves as France were held to a 1-1 draw by Albania in Rennes.
The goalkeeper denied Ledian Memushaj twice and tipped an Elseid Hysaj shot around the post as Antoine Griezmann rescued the draw for the Euro 2016 hosts with a 73rd-minute equaliser. Mergim Mavraj earlier opened the scoring on 41 minutes.
Meanwhile, Harry Winks came off the bench in the 62nd minute as England Under-19s beat Italy 3-0 at Rotherham's New York Stadium.
Emmanuel Adebayor is in Africa Cup of Nations qualifying as Togo take on Guinea and Filip Lesniak's Slovakia Under-19s face the final match of UEFA U19 qualifying against Hungary.
Kenny McEvoy is with Republic of Ireland Under-21s for a friendly against USA while Josh Onomah and Kyle Walker-Peters are in the England Under-18 squad to take on Poland.