Tranmere had goalkeeper Scott Davies to thank as they held on for a goalless draw at Cambridge.
The U's enjoyed the majority of the chances, especially before the break.
David Amoo's shot from the edge of the box was parried after 15 minutes, with Davies getting up to save well to deny Jabo Ibehre's rebound.
At the other end, James Norwood latched onto a long ball out of defence but his progress was stopped by a terrific block by Cambridge defender George Taft.
Rushian Hepburn-Murphy chased down the right channel and flicked a shot across Davies and wide.
In the final 10 minutes of the first half Davies twice kept Cambridge out, saving from Ibehre after Zoumana Bakayogo's wayward back-pass, before instinctively keeping out Hepburn-Murphy's point-blank header from Jevani Brown's corner.
The second half was a more cagey affair, with a Gary Deegan shot for Cambridge which cleared the crossbar the only real opening as they remained seven points above the drop zone.