The South African made six birdies, a double bogey and a bogey, leaving him at 12-under 132 halfway through the European Tour event. Els, a two-time winner of the British Open and U.S. Open, opened with a 63 Thursday.
''There's so much golf to be played. If you fall out of the lead, if you're not leading after three rounds, it doesn't really mean much at all late Sunday,'' Els said. ''So you just want to stay in the race and keep trying to go forward.''
He was followed by Matthew Baldwin of England (69) and Alexander Levy of France (68). Defending champion Danny Willettof England shot a 65 for the day's best round and was tied for fourth place with Bernd Wiesberger of Austria.
Willett was six strokes off the pace after an opening 69 and is happy he is back in contention to become the first player to defend the title in the 25th year of the event.
''Yesterday was a bit hit and miss, a little bit shaky,'' said Willett, whose season was disrupted by a back injury. ''I haven't played a lot of tournament golf in the past 14 weeks, so it was a bit rusty. And today I hit some proper golf shots again and I played really nicely.''
''The gap between Ernie and me, it's shrank by one. Instead of four, it's only three now,'' said Siem, who received great support from the appreciative crowd. ''The people were super cool today.''
Els was behind Willett and Wiesberger by the time he teed off in the afternoon. Els began with five successive pars before holing his first birdie, but ran into trouble when he found water from the tee at the par-four No. 7 and needed six shots.
After four more birdies, a bogey on No. 16 appeared to have cost him the lead but he finished with a simple tap-in for another birdie.
''I didn't feel a lot of energy today for some reason, especially on the front nine for the first 12 holes or so,'' Els said. ''I don't know, maybe it's the jet-lag or age or something. I made an absolute mess of two holes – 16 was just an absolute mess and seven. You take those really big mistakes away and then I had a really good round.''