Niall O'Connor looked to have earned the westerners their first win of the competition when his 72nd minute penalty put the visitors 19-16 up, but replacement centre May then sailed past two defenders for the decisive score.

Tiernan O'Halloran, who had another impressive outing, and Tim Taylor had earlier traded first half tries, while O'Connor kicked four penalties and Taylor and Freddie Burns combined for three for the hosts.

May's late intervention was a bitter blow for Eric Elwood's supremely committed side, who were unlucky to lose after being the better team for much of the match against an out-of-sorts Gloucester.

The hosts lacked penetration and were behind for most of the match, too often kicking possession aimlessly away with Mike Tindall and Taylor the worst culprits.

Connacht made the better start and had the first opportunity for points, but the otherwise excellent O'Connor was short with a 55-metre penalty attempt.

Gloucester soon responded with an exhilarating run from James Simpson-Daniel and, when Connacht were penalised, Taylor kicked his side into a seventh-minute lead with a simple penalty.

However, Connacht continued to be the better side in the opening exchanges and hit Gloucester with the opening try of the game after 11 minutes.

Eliota Fuimaono-Sapolu's attempted pass just inside his own half was intercepted by scrum half Frank Murphy, who combined cleverly with Gavin Duffy and George Naoupu before O'Halloran collected the final pass for a superb try which O'Connor converted.

Stung by the unexpected reverse, back came Gloucester. After a fumble from Duffy, Simpson-Daniel narrowly failed to win the approval of television match official Gareth Simmonds for a touchdown.

However, from the resulting five-metre scrum, Taylor ran strongly to force his way his over for a try which he converted himself.

The visitors responded with an excellent counter attack featuring powerful runs from Eoin Griffin and O'Halloran and, when the hosts were penalised, O'Connor tied up the scores after half-an-hour.

Some clever tactical kicking from Duffy and O'Connor kept Gloucester on the back foot and the men in green regained the lead with a 37th minute penalty from O'Connor to enable them to hold a deserved 13-10 interval advantage.

Certain sections of the crowd were dissatisfied with the Gloucester performance in the first half and, on the restart, Burns was introduced at out-half in place of Taylor.

But there was to be no quick remedy as once again Connacht, with the returning Johnny O'Connor and John Muldoon driving them on up front, began well and extended their lead with another O'Connor penalty.

Further home changes saw Rory Lawson and Akapusi Qera enter the fray and, spurred on by impressive efforts from Simpson-Daniel and Olly Morgan, there was more urgency in Gloucester's play and they brought the deficit back to three points with a penalty from Burns.

Connacht should have nullified that score but O'Connor missed with a 20-metre drop goal attempt and Elwood's men were soon made to pay as a second penalty from Burns made it 16-16 with just 11 minutes remaining.

Another fine attack down the right, as Duffy's inside pass unleashed O'Halloran through a gap, could have led to a try for the province. O'Halloran showed good awareness to link with replacement Kyle Tonetti but he was hauled down before he could reach for the right corner.

It did give Connacht a good territorial position and when Gloucester were subsequently penalised, O'Connor fired over a straightforward penalty and a memorable victory for Connacht seemed likely until May's decisive seven-pointer.

Speaking afterwards, Elwood said: "The dressing room is very quiet, we played extremely well and to lose in the way we did is difficult to take. We've got to keep bouncing back and though it's tough going it hasn't broken our spirit.

"We didn't play our best last week, especially up front but today the forwards fronted up magnificently and gave us a platform from which we could play."