Gareth Bale scored a 30th-minute goal for Wales against Serbia in Cardiff in a key Group D game, but Aleksandar Mitrovic levelled five minutes from time when his header went in off the post and Wayne Hennessey.
Ireland went to the top of the group with a 1-0 win over Austria in Vienna. James McClean struck the winner three minutes after the break to give Ireland a first win over Austria in 53 years and a first ever victory on Austrian soil.
It was also Austria's first defeat in four years in the Ernst Happel stadium, leaving Marcel Koller's side with an uphill task now to make the finals in Russia.
Ireland move to 10 points from a possible 12, while Serbia advance to eight and Wales to six. Austria languish on four points while Georgia are on two after being held 1-1 by visiting Moldova, who earned their first point.
"There are no world class teams in this group, we will all take points off each other so to win in Austria is no easy feat. We are delighted," McClean said.
Koller said his team failed to take two good scoring chances before halftime and were then punished on a counter-attack after the interval.
"We are not scoring. It's just small things," he said.
"The important thing is we still have six games and there are 18 points available. It will be tight, we'll have to get even more together."
Croatia top Group I after a 2-0 win over Iceland, with Marcelo Brozovic opening after 15 minutes and scoring the second in stoppage time.
Turkey defeated Kosovo 2-0 thanks to goals shortly after the break by Burak Yilmaz and Volkan Sen.
Croatia move to 10 points, two ahead of Ukraine, who defeated Finland 1-0, with Iceland on seven and Turkey on five.