With the Sheffield venue almost full, both players exchanged regular blows as Selby battled back to open up a slender 8-7 advantage.
Murphy, crowned king of the Crucible as a 22-year-old qualifier in 2005, led for much of the final’s opening day but a characteristically gutsy performance from Selby, 37, kept the world No 7 at arm’s length.
Three-time world champion Selby had toppled Stuart Bingham in a 17-15 thriller the previous evening and showed signs of fatigue with a slow start yesterday afternoon.
Murphy, 38, came out of the blocks the quicker of the pair and hauls of 57 and 67 points – despite no breaks of note – propelled him into a 2-0 advantage.
World No 4 Selby battled back in typically defiant fashion, however, as he pinched an edgy third frame – in which Murphy made a 65 break – before a fluent 89 in frame four levelled the scores.
Murphy, who blew away 2020 runner-up Kyren Wilson 17-12 in his Saturday semi-final, hit back with a fine visit of 75 in the fifth but Selby notched a total of 66 points in the sixth to restore parity again.
The Crucible was around 60 per cent full during the afternoon and the crowd were soon treated to a fluent final two frames of the session from Murphy, who rattled in breaks of 64 and 52 to haul himself into a 5-3 lead heading into the evening.
More fans had bought tickets for the evening session and with the storied Sheffield venue almost at capacity – blazing a trail for other events to follow – it was Selby who struck first to reduce the deficit.
He knocked in a majestic break of 85 but Murphy, playing in his fourth World Championship final, responded well when a fine 98 of his own re-established his two-frame advantage.
But Selby, a 19-time ranking event winner, hit back as consecutive visits of 67 and 86 made it six frames apiece at the mid-session interval.
A visit of 64 from Murphy then restored his narrow lead before Selby, world champion in 2014, 2016 and 2017, made a gutsy 57 of his own to bring about parity again.
And he took the lead for the first time in the match in the 15th frame as a fluent, free-flowing 90 left Murphy slumped in his chair.
The Sheffield showpiece is tantalisingly-poised heading into Monday’s Bank Holiday finale and six-time world champion Ronnie O’Sullivan, who was stunned by Anthony McGill in the last 16, believes Selby’s in the driving seat.
Speaking on Eurosport at the evening mid-session interval, O’Sullivan, 45, said: “Selby’s looking really comfortable with knowing what his opponent can and can’t do. He knows where his game’s at.”
Watch the World Snooker Championship live on Eurosport and Eurosport app from April 17- May 3
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