The five-time world champion’s place in the York Barbican tournament was in doubt when he suffered a broken left ankle while out running.
He limped through his first-round match with Daniel Wells, with a protective brace on, but looked a lot healthier last night after receiving treatment from the Blades’ physiotherapists.
O’Sullivan – who practises at the Star Snooker Academy, which is sited at United’s training ground – was not at his fluent best in the early stages, as Lines spurned several chances to grab an early lead.
But the 44-year-old Yorkshireman, who reached the quarter-finals of the UK finals five years ago, could not profit as O’Sullivan powered into a 3-1 lead at the interval.
Before the match, O’Sullivan had Tweeted: “Gonna give the ankle a go for my 2nd round @WorldSnooker1 match at 7pm tonight. Thanks to @SUFC_tweets Physio team for looking after me.”
Lines – watched by son Oliver, a first-year Tour professional himself, in the Barbican crowd – must have wished the Blades had not done such a fine job, as the world No 61 struggled to get a foothold in the contest to trail 3-0.
He at least knocked in a break of 45 to get some points on the board, his highest break of the evening, in frame four but ran out of position after knocking in a blue.
With just pink and black remaining, O’Sullivan was unable to claw back two snookers to leave Lines with something to smile about.
Refreshed after the mid-session break, O’Sullivan knocked in a 106 break to finally show a glimpse of his imperious best.
Lines had several chances to cut the deficit in a scrappy frame six, but instead of 4-2 O’Sullivan pinched it to edge 5-1 ahead, needing just one more frame for victory.
But Lines – who pocketed £3,000 in defeat – was not going down without a fight, finding form to win back-to-back frames.
A 41 clearance had the makings of a 147 maximum but he faltered on the sixth black. It was enough to win the frame, though, for Lines, who then made a 54 break in frame eight.
O’Sullivan clinched a 6-3 victory with a 74 break.
“For the first four frames before the interval I just couldn’t settle down,” said Lines. “I don’t know if the occasion got to me.
“I had plenty of chances, I have no complaints. The better man definitely won. If you don’t take your chances, you get punished, and I did.
“York is a fantastic venue. To play Ronnie was really enjoyable, it’s just a shame I came up short.
“I had a lot of chances in the first frame, and when I didn’t win that it just escalated. The pressure builds, I didn’t settle down until I had virtually lost (at 5-1) and I relaxed.
“If I could have done that from the off, I could have probably done a lot better.
“I was definitely going for the maximum, I had lost by then, and was just going for it.”
O’Sullivan was full of praise for his opponent.
“Well done to Peter, he’s had a good season and played some good stuff,” said O’Sullivan
“Thank you to Sheffield United for helping me out.
“It’s bad timing for me, but I just need to battle on.”
Of eight Yorkshire players who started out at York, only Lines and Sheffield’s Joel Walker reached the second round.
Walker beat former Masters champion Alan McManus at the first hurdle, to earn a meeting with Tom Ford last night.
The pair shared the opening four frames before 20-year-old, Walker, who reached the quarter-finals of the Welsh Open last season, pulled away after the interval to win 6-3 and set up a third-round date with Stuart Bingham.
Earlier, defending champion Neil Robertson survived a potential upset as the Australian battled back from 5-4 to beat Kyren Wilson 6-5, while Shaun Murphy beat Finland’s Robin Hull 6-3.
But world champion Mark Selby saw his challenge end, losing out to David Morris.
Selby was able to head home to Leicester to see wife Vikki and their daughter Sofia, who was born on November 11, and spend some welcome family time together.
“At least I can go back home and spend as much time as possible with my daughter,” said Selby, after a surprising 6-4 second-round defeat to the 26-year-old from Kilkenny.
Defeat means Selby will concede his No 1 ranking spot to either Robertson or Sheffield-based Ding Junhui, the latter beating Jimmy White 6-2.
Mark Allen crushed Belgian teenager Luca Brecel 6-0.
Other winners yesterday included Peter Ebdon, Stephen Maguire and Ken Doherty.