The Saints began strongly and were all over the visitors early on but were unable to find a way past Alex McCarthy in the Ipswich goal.
Ipswich had their first chance midway through the half but Jay Emmanuel-Thomas, often dangerous from distance, saw his 20-yard effort tipped round the post by Kelvin Davis.
Just minutes later Southampton almost had the lead after a free-flowing move, but Adam Lallana couldn't shoot past McCarthy and Ipswich held out to half time.
Paul Jewell's men began the second 45 in an improved manner and might have been ahead but for Davis who denied the in-form Michael Chopra.
Lambert could have put the game to bed minutes later but shot wide and was soon punished by 77th-minute substitute Jason Scotland.
The forward cut inside from the right and his shot took a slight deflection on its way past Davis.
A point still means that Nigel Adkins's men are two clear of West Ham, who have two games in-hand, at the Championship's summit. Meanwhile, Ipswich drop a place to 15th despite the draw.