The Lions made a winning start to their tour of New Zealand by beating Bay of Plenty 34-20, but victory was tarnished by an injury to Lawrence Dallaglio.
The tourists were pushed hard by the home side in Rotorua and went in level at 17-17 at half-time.
But their attacking play proved decisive as they ran in six tries, with two from England wing Josh Lewsey.
Dallaglio was stretchered off after 20 minutes and is believed to have dislocated his ankle.
Lions coach Sir Clive Woodward will have been pleased with his side's attacking potency after their lucky draw against Argentina two weeks ago.
Lewsey, centre Gavin Henson and scrum-half Dwayne Peel were particularly lively, but there were missed tackles in defence and fly-half O'Gara was less than clinical with his kicking, slotting only two from six.
The Lions made a scintillating start, racing into a 17-0 lead after just 11 minutes, and O'Gara was to the fore, standing flat and marshalling his back line with great skill.
He set up Lewsey for the opening try after two minutes, the England wing finishing clinically after O'Driscoll confused the Bay defence with a decoy run.
Lewsey quickly added a second after taking a long pass from Henson and Mark Cueto grabbed a third with his first touch of the game when, unmarked on the right wing, he gathered a clever cross-field punt from O'Gara.
The home side barely knew what had hit them, but they managed to claw their way back with a try from back-row forward Colin Bourke.
O'Gara this time showed the weaker side of his game, missing a tackle on Nili Latu in the run-up to the score.
And Lions' woes increased when Dallaglio was stretchered off after turning his ankle going into a tackle.
The enforced delay seemed to inhibit the visitors and they were on the back foot for much of the rest of the half.
Bay fly-half Murray Williams, who impressed with his running and kicking, slotted a penalty and then went over for a try after a neat side-step to send the sides in level at 17-17 at half-time.
The game was in the balance at the interval, but the Lions managed to recover their composure and seize control.
O'Gara threw a long pass to send Tom Shanklin over after 52 minutes and a clever break by scrum-half Peel to send the Lions clear.
D'Arcy put the result of the match beyond doubt when he was the grateful recipient of a pass from Lewsey, who had broken the Steamers' line with another scintillating break.
O'Gara slotted the conversion, but his rate of two successful kicks from six attempts will not have impressed Woodward.
Bay of Plenty: Cashmore, Bolavucu, Bunting, McQuoid, Tahana, Williams, Senio, Davison, Lutui, Castle, Sorenson, Upton, Ormond, Latu, Bourke.
Replacements: Pareanga, Filise, Tupai, Smith, Hubbard, Moon, Stewart.
British & Irish Lions: Lewsey, Cueto, O'Driscoll, Henson, Shanklin, O'Gara, Peel, Jenkins, Bulloch, Smith, O'Connell, Kay, Hill, M. Williams, Dallaglio.
Replacements: Thompson, Sheridan, O'Callaghan, Corry, Dawson, Hodgson, D'Arcy.