Celtic were held to a thrilling draw as Dundee United extended their unbeaten run to six games and the hosts retained their four-point lead at the top of the Scottish Premiership.

It looked like Jim Goodwin's visitors might end a 34-year, 51-game wait for a win at Celtic Park when goals from Zac Sapsford and Neil Farrugia gave them a half-time lead after Camilo Duran's opener for the hosts.

But Liam Scales' equaliser ensured Celtic secured a deserved point given their second-half pressure, albeit they have won just three times in their latest nine outings.

Both sides had gone close from set-pieces before the hosts broke the deadlock - and it was no surprise that it came from Duran.

Kasper Hogh knocked the ball back into his path inside the box and his Colombian strike partner slotted it home with typical aplomb for this 12th goal of the season.

Jesse Randall was denied by Celtic goalkeeper Sam Johnstone from close range and Benjamin Nygren by Jack Walton at the other end before the game took an unexpected twist.

Sapsford, fresh from scoring the weekend winner against Aberdeen, rose in similar fashion to meet a Lyall Cameron free-kick and glance into the far corner.

Three minutes later, another Cameron free-kick bounced off Bert Esselink into the path of fellow defender Farrugia to prod home his first United goal off the despairing Liam Scales.

Two half-time changes turned the tide back in Celtic's favour.

With Hogh and Callum Osmand withdrawn by manager Martin O'Neill and Haissem Hassan and Jota recruited on the wings, the latter's inswinging cross following a corner was glanced inside the far post off the head of Scales.

Celtic piled on the pressure, but United held on for a point, although that was not enough to prevent Dundee leapfrogging them into fourth.

O'Neill - looking to celebrate a year in charge with a victory - had stayed loyal to Hogh by naming an unchanged side following Sunday win away to Hibernian.

It worked initially with the Dane setting up Duran for the opener. However, Hogh failed to threaten to add to his 11 goals this season and was hooked at half-time.

The introduction of wingers Jota and Haissem Hassan for Callum Osmand and Hogh - with Duran pushed through the middle - turned the game in Celtic's favour.

However, they were unable to make the pressure count.

Celtic's nine wins in 11 home league games since the start of March is still more than any other Premiership side and their 23 in 30 this calendar year is also five more than any of their rivals.

However, despite still being in pole position at the top of the table, a run of one win in their latest five home games will be a concern, albeit their three defeats came against Ferencvaros, Rangers, Celta Vigo.

Much has been made of Goodwin's admission that Jens Berthal Askou's success with Motherwell last season had forced a stylistic rethink and his side are, at times, starting to display a similar swagger.

O'Neill, who was manager way back when the Irishman was a Celtic youth, also spoke glowingly pre-match of "gentleman" Jim's abilities as a coach.

Goodwin certainly appears to have got his tactics right as his one change from the weekend win over Aberdeen - Farrugia replacing Daniel Bennie - proved astute as he put United ahead with his first goal for the club in his first start of the season.

Style was ditched for desperate defending in the second half as they failed to end that Celtic Park hoodoo and relinquished fourth place to city rivals Dundee.

However, United have now only lost once in their latest four meetings with Celtic - and not many Premiership managers can say that.

Celtic manager Martin O'Neill: "I thought second half we were very, very strong - and yet maybe we could have conceded. We could have scored a couple of other goals.

"We fell asleep and conceded the goal, then another one. Half time allowed us to regroup and I thought the second half was very strong.

"[Haissem] Hassan has caused havoc in the second half and we should be getting on the end of one or two. I think we just have to move on and it's a big match against Falkirk on Sunday."

Dundee United manager Jim Goodwin: "I think I've got to be pleased with the overall performance.

"Of course there is an air of disappointment in the dressing room that we weren't able to hang on and take all three points.

"It would have been a historic victory had we done that, but credit to the opposition, their changes at half time brought a real spark to their team. I can't have too many complaints about the end result."