Harry Wilson curled home a stunning free-kick as a depleted Wales side beat the Republic of Ireland in the Nations League.
The Derby winger left keeper Darren Randolph rooted to the spot as his 58th-minute strike secured a 1-0 victory for a Wales team without Gareth Bale and Aaron Ramsey.
The win moves Giggs' side top of Group B4.
A win over Denmark next month in Cardiff would guarantee Wales finish top of the group and secure promotion to League A.
Until the goal, an error-strewn game had lumbered along in mundane fashion but once they had their noses in front, Giggs' youngsters rarely looked like surrendering their lead as the Republic's lack of creativity was once again cruelly exposed.
Shorn of star men Bale, through injury, and Ramsey following the birth of his twins - the first time one of the two had not featured in a competitive game since the latter made his debut in 2008 - Giggs put his faith in 18-year-old midfielder Matthew Smith and striker Tyler Roberts, just a year older.
He sent out his team to play just as they had done in thrashing Ireland 4-1 in Cardiff last month but where they had been slick and incisive on home turf, they lacked the precision to repeat their heroics in the first half at the Aviva Stadium - with the experienced Joe Allen a notable exception.
It was perhaps fitting that the game's first chance came courtesy of a ninth-minute error when Smith served up possession to Cyrus Christie on the edge of the box, although the Fulham man was unable to profit as keeper Wayne Hennessey dived to his left to keep out a low curling effort.
Both sides were guilty of surrendering the ball at regular intervals to kill their own impetus, and it was not until the closing stages of the half that either threatened again.
Tyler Roberts diverted a Connor Roberts cross straight to Randolph nine minutes before the break and Shane Duffy troubled Hennessey no further at the other end after meeting Jeff Hendrick's corner.
Callum Robinson, drafted in for the injured Callum O'Dowda, was the one man who looked capable of making the difference for the home side and he saw a goal-bound 41st-minute shot blocked by Smith's lunge.
If anything, the quality of football dropped as the second half got under way with both sides criminally careless in possession, but that all changed as Wales took the lead after Ireland shot themselves in the foot.
Harry Arter's clumsy challenge on Connor Roberts 22 yards out handed Wilson the chance to test Randolph and the keeper took a fatal step behind his wall as Wilson curled a left-foot shot into the top corner.
Ireland's response was concerted, but largely without finesse, although Hennessey had to save from Hendrick when he drilled in a rising 66th-minute effort from Matt Doherty's lay-off.
However, the visitors almost doubled their advantage from a 73rd-minute counter-attack sparked by Tom Lawrence and David Brooks, while James Chester should have hit the target from point-blank range from the resulting corner. Substitute George Thomas was denied a second goal by Randolph in stoppage time.