Jonny Williams' first international goal handed Wales a 1-0 win in Bulgaria to stay on top of Nations League Group B4, but Stephen Kenny remains winless as Republic of Ireland manager after a 1-0 defeat in Finland.
Ryan Giggs's men were without a host of key players, including Gareth Bale and Aaron Ramsey in Sofia.
But a third late winner in four games in the Nations League kept them one point clear of Finland at the top of the table.
Williams came off the bench to net the winner five minutes from time as he met Neco Williams' fine cross.
Wales and Finland face each other in Cardiff next month and will fight it out to win the group after the Finns kept the pressure on with victory over Ireland.
In front of 8,000 fans in Helsinki, Fredrik Jensen scored the only goal, as he did when the sides met last month in Dublin.
Kenny is now winless in five matches in charge and his philosophy for Ireland to play more possession football backfired for Jensen's winner.
Goalkeeper Darren Randolph's pass was intercepted by Teemu Pukki and he squared for Jensen, who scored at the second attempt after his first effort was blocked by Shane Duffy.
Centre-back Duffy remains the only man to score in Kenny's reign as for the fourth straight game Ireland failed to find the net.
Enda Stevens hit the crossbar in the second-half and Ronan Curtis was denied by a fine save from Lukas Hradecky in stoppage time.