Spain's Jon Rahm shot a 6-under 65 in Saturday's third round to cut his lead at the Spanish Open to two strokes.
The three-time former champion held back three strokes from leader Angel Hidalgo, who shot 68 to move him to 13 under for the championship.
Lahm will join Spanish compatriot Hidalgo in Sunday's final match at Madrid's Villa Campo club.
David Puig, also from Spain, is one shot behind at 11 under after a 65, while England's world number 184 Joe Dean and American Ryder Cup player Patrick Reed was 8 under.
Rahm was only allowed to play after appealing against a fine imposed by the DP World Tour for participating in the Saudi Arabia-funded LIV golf tournament.
The 29-year-old two-time major champion will need to play four tournaments each season to retain his European Tour membership, a necessary consideration for the 2025 Ryder Cup team.
He has already competed at the Paris Olympics, which is considered a DP World Tour event, as well as next month's Dunhill Links Championship in Scotland and the Andalusia Masters in Sotogrande, Spain.
The DP World Tour season ends in November.
