RiskMetrics said Tuesday it is backing hedge-fund investor William Ackman and former Starbucks Corp. (SBUX) Chief Executive James Donald to join Target Corp.'s (TGT) board, bringing Ackman one step closer to at least a partial victory in his proxy battle with the retailer.

Ackman, founder of Pershing Square Capital Management, is bidding for five seats on Target's board, and has received tepid support from other proxy advisory firms. However, RiskMetrics' decision carries much more influence, as it advises a much larger percentage of shareholders than its competitors.

RiskMetrics recommended only Ackman and Donald for Target's board, rejecting Pershing Square's other three nominees and not selecting any of Target's, because of a technicality involving proxy cards amid attendance at the shareholder meeting.

The advisory firm said Ackman's other three nominees, who have expertise in corporate governance, credit cards and real estate, respectively, shouldn't be elected because Ackman himself has some knowledge in all three of those areas.

Target hasn't approved what's called a "universal proxy card," so RiskMetrics said it couldn't support any specific Target incumbents. If it were able to, the firm said it would recommend re-electing incumbent Mary N. Dillon, a McDonald's Corp. (MCD) marketing executive, and voting against incumbents George W. Tamke, partner at private-equity firm Clayton, Dubilier, and Solomon D. Trujillo, chief executive of Australian telecom company Telstra Corp. (TLSYY).

Because the two slates are on separate proxy cards, shareholders must attend Target's May 28 shareholder meeting in order to pick and choose among the company's and Ackman's nominees. If they don't attend, they can only select from Target's white proxy card, or Ackman's gold card.

Three other proxy-voting advisory firms have already weighed in, with Proxy Governance supporting two of Ackman's nominees, Donald and real-estate industry veteran Michael Ashner. Egan-Jones backs none of Ackman's nominees but says holders should withhold votes for two of Target's incumbents, while Glass Lewis & Co. said Tuesday it is backing all four of Target's nominees.

In a statement, Target Chairman, President and Chief Executive Gregg Steinhafel praised Glass Lewis, but said of RiskMetrics, "We believe that [it] reached the wrong conclusion and one which is inconsistent with its own policies."

Target said RiskMetrics went against the firm's own "two-pronged framework" for analyzing proxy contests, which places the burden of proof on a dissident to prove board change is warranted, and that the dissident nominees are likely to make positive changes at a company.

Meanwhile, RiskMetrics is backing Ackman's contention that the Target board should have 13 members, joining Proxy Governance. Glass Lewis backed Target's proposal to fix the level at 12, along with Egan-Jones.

Corporate-governance experts have said the RiskMetrics report is the one everyone was watching for. RiskMetrics typically advises more than 20% of shareholders, while Proxy Governance and Egan-Jones combined advise less than 10%. Charles Elson, director of the Weinberg Center for Corporate Governance at the University of Delaware, last week called those endorsements "tepid at best," saying, "The real question will be answered by RiskMetrics."

Ackman's Pershing Square owns more than 7% of Target through stocks and options, and has lost hundreds of millions of dollars for himself and investors in the process. He has lobbied for many changes at Target, including a transaction to capitalize on its real estate, and a reduction to its credit-card exposure.

"Together with the recommendation of Proxy Governance last week, this confirms the clear need for meaningful change on Target's board," Ackman said in a statement.

Ackman launched the proxy battle in March after Target rejected his proposal to create a real-estate investment trust out of the land Target owns under its stores.

RiskMetrics said, "We acknowledge that one of the motivations of Pershing to engage in the proxy fight could be to 'save face' for the money Pershing lost investing in Target, but question whether that motivation should preclude the support of Pershing's fellow shareholders. It would be curious to justify full support for a board that oversaw the short-term value destruction that allegedly led to the proxy fight."

The discount retailer's results have slid during the recession as shoppers shun discretionary purchases for low-priced basics.

Glass Lewis, while noting Target "appears to be struggling in this recent downturn" with sales down for more than a year, said, "We are not convinced that the company is in need of a shakeup" at the board level. Glass Lewis also doubted Ackman's contention that his slate's retailing experience is superior to the current directors' and added that his presence on the board at struggling Borders Group Inc. (BGP) "has done little to create shareholder value."

Target's shares closed Tuesday up 17 cents, at $41.94.

-By Joseph Checkler; 201-938-4297; joseph.checkler@dowjones.com

(Kevin Kingsbury and Kerry E. Grace contributed to this story.)