Southampton needed a Stuart Armstrong wonder attack and an extended goal from Kyle Walker-Peters to overtake Coventry 2-1 in the FA Cup at St Mary’s.
Coventry, 11th in the Championship, led through a fine goal in the first half from Viktor Gyokeres and had chances to be even further ahead.
A mix-and-match Saints team with 17-year-old debutant Thierry Small as left-back and Shane Long and Theo Walcott – with a combined age of 67 – in attack, was second-best throughout the first half.
But after the break, Armstrong produced a magnificent long-range effort to take the game into overtime, and then the second break of the break, Walker-Peters, fired them into the fifth round.
But Coventry may feel tough after going toe-to-toe with the Premier League team for long periods.
In the opening moments, Josh Eccles ‘low drive from the edge of the area forced the Saints’ goalkeeper Willy Caballero to a sharp diving save.
The Saints were denied an opening in the 12th minute when Adam Armstrong pulled the ball back to Walcott, whose first shot was smashed brilliantly away by City goalkeeper Simon Moore.
Small had a heart-to-mouth moment when he misjudged a clearing with his head and was relieved to see the ball fly directly into the arms of Caballero.
But veteran goalkeeper Caballero was powerless to stop Coventry from taking a lead in the 22nd minute through a classic Gyokeres goal.
The Swedish striker exchanged passes with Ben Sheaf on the edge of the box before putting an accurate finish into the corner of Caballero’s net.
The sky blue could have been out of sight at the break, with Ian Maatsen volleying narrowly over from a corner and then drilling a low effort just over.
Nathan Redmond, on as a replacement for the injured defender Lyanco, had a chance to shoot the Saints out before the break, but Moore, who was released by Southampton at the age of 12, kept his shot.
At the break, Saints boss Ralph Hasenhuttl sent Walker-Peters after Small and Armstrong after his ineffective namesake Adam.
Michael Rose had an instant chance to bring Coventry two ahead, but headed a corner from Gustavo Hamer.
Instead, Armstrong conjured up a memorable goal to raise the top side level.
The Scottish midfielder picked up the ball 25 yards out around the right corner of the penalty area and sent the sweetest shots with the outside of his boot over Moore and into the opposite corner.
At the start of extra time, another Southampton substitute, Chelsea striker Armando Broja, ran down the right but could only find the side netting.
But with 112 minutes on the clock, Broja found Walker-Peters down on the left and he ran towards Todd Kane in the area before sending a deflected effort past Moore.
Even then, Coventry had chances to take the equalizer to penalties, but Martyn Waghorn put a header at the far post and got a goal rejected for offside as the Saints scraped through.
When is the FA Cup drawn in the fifth round?
The draw for the FA Cup in the fifth round is on Sunday 6 February.
It will take place before Liverpool’s home clash with Cardiff around 11.30am and you can follow it live on the Sky Sports app and website.