The Kreb's Cycle (Citic acid cycle - KC) is a series of chemical reactions through the oxidaction of acetyl-CoA, while glycolysis is a linear chain reaction for the oxidaction of glucose.
In the Krebs cycle we have the production of 3 NADH's and 1 ATP (GTP) per turn, while in glycolysis we have 2 ATP's and 2 NADH's. But when we compare the breathing process as a whole we have a final balance of 2 ATP's coming from Kreb's Cycle, 2 from glysolysis and 28 from the electrochemical chain. The potencial of the ATP production in each process depends of the capacity that the NADH to enter the mitochondria and the fact that the pyruvate produced in the glycolysis can enter in the KC and accelerate the production of ATP in the KC even before glycolysis. One pyruvate can produce two molecules of Acetil-CoA and that can make two turn in the KC (6NADH's that can go in the electrochemical chain, with 2 ATP's molecules), but in glycolisis the pyruvate is comsumed in only 2 ATP's per molecule and 2NADH.